IP* 


Frontispiece. 


BjOTANY 


FOR    HIGH    SCHOOLS 


BY 
GEORGE    FRANCIS    ATKINSON,  Pn.B. 

PROFESSOR   OF    BOTANY    IN    CORNELL    UNIVERSITY 


OF   THE 

UNIVERSITY 


NEW 

HENRY    HOLT    AND    COMPANY 
1910 


APR    5   1911 
GIFT 


COPYRIGHT,  igio 

BY 

HENRY   HOLT  AND   COMPANY 


Stanhope 

F.    H.   GILSON     COMPANY 
BOSTON.     U.S.A. 


PREFACE. 


THIS  book  is  addressed  to  pupils  in  their  first  or  second 
year  in  the  high  school.  It  assumes  that  Botany  may  be  the 
first  science  they  study,  and  that  therefore  it  should  provide 
plenty  of  individual  work  within  their  powers,  and  should 
give  this  work  unity  of  effect  and  make  it  evidently  worth 
while.  In  keeping  with  the  modern  scientific  spirit,  nutrition, 
reproduction,  and  relation  to  man  are  made  the  dominant 
aspects  of  the  subject.  What  plants  are  is  made  to  appear  in 
terms  of  what  they  do.  Structures  and  processes  are  Ithen 
interpreted  both  from  the  plant's  point  of  view  and  from  man's. 
The  problems  set  before  the  pupil  call  for  definite  and  con- 
tinued effort  on  his  part,  and  for  the  independent  interpreta- 
tion of  observations.  The  economic  relations  of  plant  life  are 
noted  as  the  study  proceeds,  and  the  concluding  chapters  are 
intended  to  leave  the  pupil  with  a  general  view  of  the  larger 
general  applications  of  the  science. 

Especial  importance  is  given  to  the  study  of  seeds  and  seed- 
lings, the  parts  of  the  full-grown  plant  and  the  principal  types 
or  forms  of  the  root,  stem  and  leaf,  including  the  work  per- 
formed by  these  parts  in  providing  food  and  water,  building 
material,  and  food  storage.  Since  the  flower  is  an  important 
structure  designed  for  the  purpose  of  facilitating  seed  produc- 
tion, with  principal  and  subordinate  organs  for  this  work, 
especial  interest  is  attached  to  a  careful  study  of  its  parts  and 
their  structure.  As  the  different  kinds  of  flowers  and  the 
different  modes  of  their  association  on  the  flower  shoot  are 
the  result  of  the  operation  of  natural  laws,  floral  structures 
and  groupings  naturally  indicate  plant  relationship.  Several 
of  these  different  types  are  therefore  studied,  not  for  the 

211254 


VI  PREFACE 

primary  purpose  of  plant  analysis  leading  to  the  naming  of 
plants,  but  in  order  to  stimulate  the  student  to  recognize  some 
of  the  general  facts  indicating  the  bond  which  unites  the 
very  diverse  elements  of  the  natural  world.  This  should  be 
one  of  the  chief  aims  in  all  studies  of  nature,  not  because  it 
is  the  scientific  method,  but  because  of  the  unconscious  and 
wholesome  influence  which  it  has  upon  the  formation  of  char- 
acter and  the  development  of  a  taste  for  the  things  beautiful 
in  nature,  in  art,  and  in  life's  best  work. 

Several  chapters  are  devoted  to  a  study  of  the  peculiar  and 
unusual  forms  of  nutrition  by  certain  plants  that  have  become 
closely  associated  in  this  respect  with  other  organisms,  and  by 
the  fungi  and  bacteria,  which,  lacking  chlorophyll,  must  obtain 
certain  food  by  other  means  than  that  employed  by  the  green 
plants.  In  this  connection  special  attention  is  given  to  some  of 
the  more  important  micro-organisms  which  are  beneficial  to 
man  because  of  certain  products  of  their  activity,  or  which  are 
harmful  as  causal  agents  in  disease.  One  chapter  is  devoted 
to  the  study  of  the  more  useful  plants  of  the  farm,  orchard 
and  garden  or  of  those  employed  in  industrial  operations. 
Chapters  are  also  devoted  to  the  principles  of  plant  develop- 
ment and  plant  breeding,  subjects  which  are  of  absorbing  inter- 
est to  all  and  of  special  practical  importance  to  the  farmer  and 
horticulturist. 

In  schools  where  attention  can  be  given  to  a  study  of  rep- 
resentative plants  in  the  different  branches  of  the  Plant 
Kingdom  (in  most  schools  at  least  a  few  can  be  studied)  the 
chapters  on  the  algae,  fungi,  mosses  and  ferns  will  furnish  the 
material  and  outline.  Footnotes  at  the  beginning  of  these 
chapters  suggest  one  or  two  plants  in  each  group  which  can  be 
studied  where  there  is  not  time  for  all.  In  these  chapters 
several  more  plants  are  treated  than  can  under  ordinary  cir- 
cumstances be  studied  in  the  high-school  course.  Their  inclu- 
sion in  the  book,  however,  aids  in  rounding  out  the  subject,  and 
in  most  cases  they  will  serve  a  purpose  for  special  assignment 
for  reading,  or  for  reference  or  for  illustration. 


PREFACE  Vii 

Chapters  XXXIV  and  XXXV,  on  the  Gymnosperms  and 
Angiosperms,  as  well  as  the  latter  portions  of  the  chapters  on 
the  algae,  fungi,  mosses  and  ferns,  are  not  intended  for  study 
except  in  advanced  classes.  Some  few  students,  however,  will 
be  interested  in  the  life  histories,  with  the  illustrative  formulae 
and  graphic  representations  of  life  cycles,  together  with  the 
reviews  showing  progression  in  the  evolution  of  plant  struc- 
tures. The  author  believes  it  is  a  good  principle  in  pedagogy 
to  present  now  and  then  ideas  and  inferences  upon  the  work 
which  may  be  beyond  the  comprehension  of  the  majority  of 
the  members  of  the  class,  of  course  without  holding  the  stu- 
dents answerable  in  any  way  for  it.  It  is  stimulating  and  sug- 
gestive to  most  students  especially  if  it  is  not  required  work, 
and  serves  now  and  then  to  lift  their  minds  out  of  the  ''hum- 
drum" of  the  regular  course.  A  few  will  catch  glimpses  of 
principles  and  processes  in  nature  which  will  be  decidedly 
beneficial  in  the  development  of  thought  and  reasoning  power. 

Since  it  is  neither  practicable  nor  desirable  to  lay  down  a 
hard  and  fast  course  for  all  high  schools,  there  are  suggested 
below  several  courses  \vhich  are  suitable  for  different  con- 
ditions. 

For  short  courses,  one  half  year  or  less:  Part  I,  and  Chapter 
XXXVI  (Economic  or  Useful  Plants)  with  parts  of  Chapters 
XXXVII,  XXXVIII  and  XXXIX.  For  a  full  half-year  course 
the  study  of  an  alga  (Spirogyra),  a  mold  (Bread  mold),  a  moss 
(Polytrichum  or  other  type)  and  a  fern  may  be  added. 

For  courses  in  agricultural  botany:  Part  I,  and  Chapters 
XXVI-XXIX  (Fungi),  Chapter  XXXVI  (Economic  or  Use- 
ful Plants),  and  parts  of  Chapters  XXXVII,  XXXVIII  and 
XXXIX. 

For  two  half-year  courses:  First  course:  Part  I,  and  Chapter 
XXXVI  (Economic  or  Useful  Plants)  and  parts  of  Chapters 
XXXVII,  XXXVIII  and  XXXIX.  Second  course:  Chapters 
XXII-XXXV.  Several  algae  and  fungi,  a  lichen,  a  liverwrort 
and  moss  (with  a  few  additional  types  for  illustration),  a  fern 
(with  several  additional  ones,  with  horsetails,  club-mosses  and 


viii  PREFACE 

quill  wort  for  illustration),  a  pine   (with  other   conifers  and 
Cycas,  Zamia  and  Ginkgo  for  illustration). 

Many  of  the  illustrations  are  new  and  were  made  especially 
for  this  book,  the  photographs  being  made  by  the  author  and 
the  drawings  by  Mr.  Frank  Rathbun  under  the  author's  super- 
vision. Acknowledgments  are  due  to  Messrs.  Ginn  and  Company 
for  the  use  of  a  few  illustrations  from  Bergen  and  Davis's  Prin- 
ciples of  Botany  and  from  the  author's  First  Studies  in  Plant 
Life;  to  D.  Appleton  &  Co.  for  the  use  of  a  few  illustrations 
from  Coulter's  Botany;  and  to  the  Bureau  of  Forestry  and  the 
Bureau  of  Plant  Industry,  U.  S.  Dept.  of  Agriculture,  for  some 
photographs  which  are  acknowledged  in  connection  with  the 
illustrations. 

G.  W.  A. 

CORNELL  UNIVERSITY,  April,  1910. 


TABLE    OF    CONTENTS. 


PART   I.     GROWTH   AND    WORK   OF   PLANTS. 

CHAPTER  I. 

PAGE 

PARTS  OF  SEEDS  AND  HOW  SEEDS  GERMINATE 

The  bean     . 

The  castor  bean     . 

The  squash  or  pumpkin    . 

Corn  seedlings  .... 

The  pine      . 

Conclusions 

CHAPTER   II. 
NATURE  OF  FOOD  STORED  IN  SEEDS  AND  OTHER  PLANT  PARTS  ...       13 

CHAPTER  III. 
GROWTH  OF  ROOT  AND  STEM  .     . 

CHAPTER  IV. 
ROOTS,  THEIR  KINDS,  MECHANICAL  WORK  AND  STRUCTURE       ...       26 

Root  system     .... 
"  Kinds  of  roots  . 

.     CHAPTER  V. 
WORK  OF  ROOTS  IN  ABSORPTION  OF  WATER  AND  FOOD  FROM  THE 

SOIL 33 

CHAPTER  VI. 

TYPES  AND  KINDS  OF  STEMS 37 

Foliage  shoot    .      .      . 
Specialized  stems   . 

Buds  or  bud  shoots 47 

Growth  of  stems 49 

ix 


X  TABLE   OF   CONTENTS 

CHAPTER  VII. 

PAGE 

STRUCTURE  OF  STEMS  AND  THE  WATER  PATH  IN  STEMS  ....  51 

Structure  of  the  stems  of  monocotyledons 51 

Structure  of  the  stem  of  dicotyledons 56 

CHAPTER  VIII. 

WINTER  CONDITION  OF  SHOOTS  AND  BUDS  ........  61 

CHAPTER  IX. 

LEAVES,  THEIR  FORM  AND  MOVEMENT    .           70 

1.  The  gross  parts  of  the  leaf 70 

2.  Form  of  leaves 73 

3.  Fall  of  the  leaf ' 75 

4.  Arrangement  of  leaves 75 

5.  Relation  of  leaves  to  light 77 

CHAPTER  X. 

LEAVES,  THEIR  STRUCTURE  AND  MODIFICATIONS 83 

1.  Structure  of  leaves 83 

2.  Modifications  of  leaves 86 

CHAPTER  XL 

WORK  OF  THE  LEAVES 90 

I.   Transpiration 90 

CHAPTER    XII. 

WORK  or  LEAVES  (continued) 97 

II.    Photosynthesis 97 

III.  Assimilation 105 

IV.  Digestion .  107 

CHAPTER  XIII. 

WORK  OF  LEAVES  (concluded) 108 

V.   Respiration 108 


TABLE   OF   CONTENTS  xi 

CHAPTER  XIV. 

PAGE 

SOME  SPECIAL  ASPECTS  OF  NUTRITION  OF  PLANTS 117 

Sources  of  plant  food 117 

Nitrification 119 

Fixation  of  nitrogen 120 

CHAPTER  XV. 

NUTRITION  OF  PARASITES  AND  SAPROPHYTES 126 

Nutrition  of  parasites 127 

Nutrition  of  saprophytes 130 

Bacteria 135 

CHAPTER  XVI. 

FLOWERS,  THEIR  STRUCTURE  AND  KINDS 140 

I.    Flowers  of  dicotyledonous  plants 142 

The  buttercup 142 

The  evening  primrose 145 

Butter  and  eggs 148 

The  sweet  pea 150 

The  sunflower 153 

CHAPTER  XVII. 

FLOWERS,  THEIR  STRUCTURE  AND  KINDS  (concluded) 158 

II.    Flowers  of  monocotyledonous  plants 158 

The  Indian  corn         158 

Jack-in-the-Pulpit,  Indian  turnip 163 

Gladiolus 165 

CHAPTER  XVIII. 

METHODS  OF  POLLINATION .  167 

Close  pollination 169 

Cross-pollination  by  the  wind 171 

Cross-pollination  by  insects 172 

CHAPTER  XIX. 

FERTILIZATION  AND  DEVELOPMENT  OF  THE  SEED    .  182 


Xll  TABLE   OF   CONTENTS 

CHAPTER  XX. 

PAGE 

THE  FRUIT 187 

1    Parts  of  the  fruit 187 

II.   Indehiscent  fruits        188 

III.  Dehiscent  fruits 191 

IV.  Fleshy  and  juicy  fruits 192 

V.   Reinforced,  or  accessory,  fruits 195 

VI.    Fruits  of  gymnosperms 196 

VII.   The  "fruit"  of  ferns,  mosses,  etc 197 

CHAPTER  XXI. 

SEED  DISPERSAL 198 


PART   II.     GENERAL    MORPHOLOGY  AND 
CLASSIFICATION    OF   PLANTS. 

CHAPTER  XXII. 

OUTLINE  OF  CLASSIFICATION 206 

CHAPTER  XXIII. 

211 

Green  algae 212 

Conjugating  green  algae 212 

Single-celled  green  algae 220 

Filamentous  green  algae 221 

Siphon  green  algae 226 

Stoneworts,  or  bass  weeds 228 

Review  of  the  green  algae 229 

CHAPTER  XXIV. 

(concluded) 231 

The  blue-green  algae 231 

The  diatoms 234 

The  brown  algae 235 

The  red  algae 239 


TABLE   OF   CONTENTS  xiii 

CHAPTER  XXV. 

PAGE 

BACTERIA 244 

CHAPTER  XXVI. 

FUNGI 246 

General  characters;  molds;  mildews 246 

Alga-like,  or  sporangium-fruit  fungi 248 

The  conjugating  molds 248 

The  water  molds 254 

The  downy  mildews  and  white  rust 256 

CHAPTER  XXVII. 

FUNGI  (continued) 261 

Sac  fungi,  or  ascus  fungi 261 

The  powdery  mildews 262 

Lilac  mildew 263 

The  black  fungi 265 

The  cup  fungi 266 

The  morels 268 

The  yeast  fungi 268 

The  lichens 270 

CHAPTER  XXVIII. 

FUNGI  (continued) 276 

The  Basidium  fungi 276 

The  smuts 276 

Rust  fungi 279 

Wheat  rust 280 

CHAPTER  XXIX. 

FUNGI  (concluded) 291 

Basidium  fungi  (concluded) 291 

The  gill  fungi 292 

Bracket  fungi  or  pore  fungi 296 

The  coral  fungi,  or  fairy  clubs 298 

The  hedgehog  fungi,  or  tooth  fungi 299 

Puffballs,  earth  stars,  etc 299 

Comparative  review  of  the  fungi 300 


XIV  TABLE   OF   CONTENTS 

CHAPTER  XXX. 

PAGE 

LIVERWORTS 304 

Thallose  liverworts 306 

The  foliose  liverworts 311 

Horned  liverworts 313 

Comparative  review  of  the  liverworts 314 

Alternation  of  generations 315 

CHAPTER  XXXI. 

MOSSES 316 

Alternation  of  generations 324 

Comparative  review  of  the  mosses  • 325 


CHAPTER  XXXII. 

FERNS 327 

Some  of  the  common  ferns 329 

Life  history  of  ferns 334 

Dimorphism  in  ferns 338 

Comparative  review  of  the  ferns 341 


CHAPTER  XXXIII. 

OTHER  FERN-LIKE  PLANTS  . 343 

The  horsetails 343 

The  club  mosses 346 

The  quillworts 350 

Comparative  review  of  the  fern  plants  .      .      . 351 


CHAPTER  XXXIV. 

GYMNOSPERMS 357 

The  life  history  of  the  pine 360 

Other  Gymnosperms •.  366 


CHAPTER   XXXV. 

ANGIOSPERMS 375 


TABLE   OF   CONTENTS  XV 

CHAPTER  XXXVI. 

PAGE 

ECONOMIC  OR  USEFUL  PLANTS 392 

Monocotyledons 392 

Dicotyledons 402 

CHAPTER  XXXVII. 

RELATION  OF  PLANTS  TO  ENVIRONMENT  OR  ECOLOGY 421 

I.    Factors  influencing  vegetative  type 421 

II.   Vegetation  types  and  structures 425 

CHAPTER  XXXVIII. 

MIGRATION  AND  DISTRIBUTION  OF  PLANTS 431 

I.    Methods  and  causes  of  plant  migration 432 

II.   Barriers  to  plant  migration 437 

CHAPTER  XXXIX. 

PLANT  SOCIETIES 439 

Forest  societies 440 

Other  plant  societies 446 


CHAPTER  XL. 

SOME  PRINCIPLES  OF  PLANT  EVOLUTION 455 


CHAPTER  XLI. 

SOME  PRINCIPLES  OF  PLANT  BREEDING 464 

I.   The  improvement  of  existing  varieties 465 

II.   The  production  of  new  varieties .467 

INDEX 479 


PART  I. 

GROWTH  AND  WORK  OF   PLANTS. 


CHAPTER  I. 

PARTS  OF  SEEDS  AND  HOW  SEEDS  GERMINATE. 
THE  BEAN. 

1.  Seed  of  the  common  garden  bean.—  There  are  many  varie- 
ties of  garden  beans  but  the  form  of  the  seed  is  often  slightly  curved 
or  kidney-shaped  as  seen  in  side  view.  Upon  the  concave  side 
there  are  distinct  markings.  There  is  a  scar  (=  hilum)  about  the 
middle  line.  This  is  the  point  where  the  seed  was  attached  to 
the  wall  of  the  bean  pod  as  can  easily  be  seen  in  the  case  of  young 
beans  by  opening  the  pods.  On  either  side  of  the  scar  is  a  minute 
mark.  One  of  these  is  slightly  larger  than  the  other  and  often 
appears  when  examined  under  a  hand  lens  to  be  somewhat  heart- 
shaped.  It  is  continuous  with  a  short  elevated  line  on  that  end 
of  the  bean.  This  slightly  elevated  line  is  the 
raphe  (fig.  i).  It  is  formed  by  the  stalk  of  the 
ovule  (the  very  young  stage  of  the  seed  in  the  pod) 
.which  is  attached  at  the  end  of  the  bean  and 
here  is  bent  around  and  joined  to  the  edge.  On 
the  other  side  of  the  scar  and  near  it  is  a  minute 
opening,  the  micropyle.  The  root  of  the  embryo 
lies  beyond  this  just  underneath  the  seed  coats.  Fig.  i. 

Its   position  is  often  manifest   by   a  prominent    ide  as  primary  root- 


elongated  elevation  especially  when  the  bean  is    Em^raphe;  c.  cha- 
swollen  after  soaking  in  water. 

3.  Parts  of  the  bean  seed.  —  When  beans  are  soaked  for  a 
few  hours  in  water  the  seed  coats  take  up  the  water  faster  than 


?  AND   WORK  OF  PLANTS 


Fig.  2. 

Bean  seeds  soaking  and  swelling;  read 
from  left  to  right. 


.consequently  swell  faster  and  become  much 
Syfinkied.  The  seed  coats  thus  become  loosened  from  the  embryo 
within  and  can  be  easily  slipped  off.  After  a  time  the  embryo 
swells  by  imbibition  of  water  and  the  seed  becomes  plump  again. 
When  the  seed  is  split  in  two  lengthwise  by  cutting  the  seed  coats 
along  the  convex  side,  the  two  halves  can  be  laid  open.  These 
two  fleshy  bodies  are  the  seed  leaves  or  cotyledons,  and  the  rest  of 

the  embryo  is  attached  at  one 
end  to  one  of  the  halves,  its  attach- 
ment being  broken  away  from  the 
other.  The  root  or  radicle  lies  at 
one  end  next  the  seed  coats  and  in 
the  entire  bean  seed  causes  the 
short  elevated  line  at  this  end 
of  the  seed.  At  the  opposite  end 
is  the  plumule,  consisting  of  two  or  four  membranous  leaves  now 
somewhat  triangular  in  form  and  marked  with  fine  lines  or  veins. 
The  stem  of  the  embryo  is  short,  and  is  that  part  of  the  embryo 
to  the  upper  end  of  which  the  cotyledons  are  attached,  and  to 
the  lower  end  of  which  the  radicle  is  attached.  This  part  of  the 
stem  is  the  hypocotyl. 

3.  Germination  of  the  bean. — In  germination  the  radicle 
elongates  more  rapidly  at  first  than 
the  other  parts,  soon  pierces  the 
seed  coat  near  the  scar  and  forms 
a  long,  slender,  conical,  primary 
root.  The  root  hairs  soon  appear, 
forming  a  dense  velvety  covering 
over  the  root  a  little  distance  back 
from  the  tip.  As  the  stem,  and 
leaves  of  the  plumule,  which  lie 
between  the  cotyledons,  increase  in 
size  the  seed  coats  are  ruptured 
by  the  pressure  and  are  usually 
cast  off  in  the  soil.  The  part  of  the  stem  which  lies  be- 
tween the  cotyledons  and  the  root  now  elongates  very  rapidly 


Fig.  3- 

Bean  seed  split  in  two,  showing  plantlet 
(radicle  and  plumule)  at  one  end. 


PARTS  OF  SEEDS:  THE  BEAN 


and  arches  up  in  the  form  of  a  loop.     It  is  this  loop  which  breaks 
the  way  through  the  soil,  since  it  would  be  a  difficult  task  for 


Fig.  4. 
Bean  seeds  germinating,  seed  coat  slipping  off. 


Fig.  5. 

Beans  germinating,  one  cotyledon  removed, 
showing  expanding  plumule. 


the   slender   stem  to  push  the  bulky  cotyledons  up  ahead  of  it. 

The  cotyledons  are  therefore 

pulled   from    the    ground    as 

the  loop  straightens  up  after 

emerging  from  the  soil.    This 

portion   of   the    stem    (hypo- 

cotyl)  becomes  quite  long  in 

the   bean,  but  is  quite   short 

in  the  corn.     The  cotyledons 

are    thus    lifted    above    the 

ground.     They  become  more 

or  less  shrivelled  and  shrunken  Fis-  6- 

,  ..  How  the  garden  bean  comes  out  of  the  ground. 

because  01  the  food  SUDStance  First  the  looped  hypocotyl,  then  the  cotyledons 

pulled  out,  next  casting  off  the  seed  coat,  last  the 

Withdrawn  tor  the  growth  Of  plant  erect,  bearing  thick  cotyledons,  the  expand- 
ing leaves,  and  the  plumule  between  them. 

the   seedling,  and  finally  fall 

away,  as  the  young  membranous  leaves  expand  and  the  stem 

elongates. 


GROWTH   AND    WORK   OF   PLANTS 


4.  In  the  scarlet  runner  bean,  and  in  the  pea,  the  hypocotyl 
remains  short  so  that  the  cotyledons  are  left  in  the  ground.     The 
portion  of  the  stem  above  the  cotyledons  elongates  and  forms  the 
loop  as  the  seedling  emerges  from  the  soil  so  that  the  tender  leaves 
and  plumule  are  not  injured,  as  they  would  be  if  pushed  up  while 
they  are  standing  erect. 

THE   CASTOR  BEAN. 

5.  The  castor-oil  bean. — The  seed  of  the  castor-oil  plant  is 
often  called  a  bean,  castor-oil  bean,  or  castor  bean,  because  it 


Fig.  7. 
Castor  bean  seeds  sprouting. 

resembles  a  bean  somewhat  in  shape. 
It  is,  however,  not  a  true  bean,  but 
belongs  to  the  Spurge  family.  At  the 
smaller  end  of  the  seed  there  is  a  mass 
of  spongy  tissue  which  covers  the  hilum. 
This  is  called  the  caruncle.  Its  func- 
tion is  to  absorb  moisture  and  thus 
provide  for  the  passage  of  water 
through  the  hilum  end  of  the  seed, 
where  it  passes  more  readily  than 


Fig.  8. 
Castor  bean   germinating. 


At 


through  the  outer  parts  of  the  hard  gUSTWStS-B.I? 
seed  coats,  which  are  smooth  as  if 

varnished,  and  not  so  absorbent  as  the  dull  more  porous  part 
of  the  coat  which  lies  under  the  caruncle.  When  the  seed  is 
cut  open  there  is  seen  a  mass  of  white  mealy  substance,  the 


PARTS  OF  SEEDS:  THE  CASTOR  BEAN       5 

endosperm,*  which  is  covered  by  a  thin  papery  material.!  The 
embryo  lies  within  the  endosperm;  its  radicle  at  the  end  next 
the  caruncle.  The  two  cotyledons  are  thin  and  covered  by  the 
endosperm. 

6.  Germination  of  the  castor  bean. — The  spongy  substance 
of  the  caruncle  becomes  much  swollen  by  absorption  of  water. 
In  germination  the  swelling  of  the  embryo  and  endosperm  by 
the  absorption  of  water  bursts  the  rigid  seed  coat  causing  it  to 
crack  lengthwise,  so  that  a  portion  of  the  endosperm  can  be  seen 
through  the  crack.  The  radicle  emerges  from  the  end  where  the 
caruncle  is  located.  The  hypocotyl,  which  is  very  short  in  the 
embryo  stage,  now  elongates.  The  seed  being  bulky  is  not  readily 


Fig.  9- 
Germination  of  castor-oil  bean. 

pushed  up  through  the  soil.  The  hypocotyl  part  of  the  stem  arches 
upward  forming  a  loop  and  as  it  elongates  and  endeavors  to 
straighten  up  it  pulls  the  "seed-"  from  the  ground.  Figure  9 
shows  different  stages.  The  hard  seed  coat  gradually  slips  off. 
The  white  endosperm  is  now  very  distinct  and  is  seen  to  cover  up 
the  cotyledons  \vhich  remain  closed.  It  can  be  seen,  however, 
that  the  endosperm  is  "  wasting  away,"  that  it  is  being  absorbed 
through  the  outer  faces  of  the  cotyledons.  By  this  means,  they  are 
exposed  to  the  light  and  take  on  a  green  color.  The  mass  of  the 
endosperm  becomes  less  and  less,  until  finally  there  is  but  a  thin 

*  The  endosperm  is  food  stored  in  the  seed  outside  of  the  embryo. 
f  This  papery  lining  is  the  dead  remnant  of  the  nucellus  which  was  used 
up  in  the  growth  of  the  endosperm.     See  Chapter  XXXV. 


GROWTH  AND    WORK   OF   PLANTS 


film  or  remnant  which  dries.  The  food  stored  in  the  seed  here 
has,  therefore,  been  completely  used  up  by  the  embryo  during  ger- 
mination, and  the  cotyledons  have  served  as  the  absorptive  organs 
for  this  food. 


Fig.  10. 

Seedlings  of  castor-oil  bean  casting  the  seed  coats,  and  showing  papery  remnant  of  the 
endosperm. 

7.  The  embryo  of  the  castor-oil  bean  presents  a  type  very 
different  from  that  of  the  bean  as  we  can  readily  see  by  a  com- 
parison. Yet  the  two  types  so  different  in  form  and  structure 
are  very  similar  when  we  consider  the  relation  of  the  food  sub- 
stance to  the  cotyledons  and  the  function  of  the  latter  in  absorption 
of  this  stored  food.  It  should  not  be  difficult  now  to  understand 
how  the  embryo  of  the  bean  and  pea  during  the  formation  of  the 
seed  can  absorb  the  endosperm  through  the  cotyledons  though 
it  is  stored  in  the  cotyledons  as  food  for  the  embryo  during 
germination  and  the  early  stage  of  the  seedling. 


PARTS  OF  SEEDS:  CORN  SEEDLINGS 


st 


side  to  the  stem  or  caulicle  and  this  point  of  connection  can  be  seen 
quite  clearly.  This  is  the  scutellum  of  the  embryo,  so  calkd  be- 
cause of  its  form  and  the  central  attachment  at  one  side  which 
resembles  a  little  shield.  The  stem  or 
caulicle,  the  leaf  bud,  or  plumule,  the* 
root  or  radicle,  the  root  sheath,  and  the 
scutellum  or  cotyledon,  make  the  .young 
embryo  in  the  corn  seed.  There  is  still 
a  large  bulk  of  the  content  of  the  grain 

Fig.  IS- 

Com  grains  sprouting;  st.    which  lies  against  the  scutellum.      This 
muie-  '/radicle  fn  °roo/sneSth     is  known  as  the  endosperm.     In  the  corn 
oot'    it  is  largely   made  up  of   starch   which 
is  stored  food  for  the  young  embryo  when  the  seed  germinates. 

12.  Germination  of  the  corn. — The  root  sheath  usually 
emerges  first  with  the  radicle  of  the  embryo  still  enclosed. 
While  the  root  sheath  is  still 
short,  lengthwise  sections  will 
show  that  it  has  ceased  to  elon- 
gate, and  the  root  has  pushed 
through  it  at  one  end. 


Fig.  16. 

Germination  of  corn  grains,  showing  origin 
of  first  lateral  roots.  Note  the  radicle  (pri- 
mary root)  emerging  from  the  root  sheath. 
In  right-hand  seedling  note  the  remains  of 
root  sheath  from  which  the  radicle  emerged. 


Fig.  17. 

Germinating  corn  grains, 
primary  root  have  emerged. 


Plumule  and 


At  this  stage  sections  also  show,  when  made  through  the  middle 
line  of  the  embryo,  the  origin  of  the  first  two  lateral  roots.  One 
of  them  lies  inside  in  the  axis  of  the  scutellum  and  the  leaf, 
while  the  other  lies  opposite  underneath  the  coat  of  the  groove 


10 


GROWTH   AND    WORK   OF   PLANTS 


(see  fig.  1 6).  They  are  really  adventitious  roots  since  they  arise 
from  the  stem.  The  true  lateral  roots  arise  from  the  primary 
root  and  extend  in  a  nearly  horizontal  direction,  and  the  branch- 
ing of  these  finally  results  in  a  great  mass  of  fibrous  roots  radiat- 
ing in  all  directions  in  the  upper  soil  layers.  About  the  same 
time  or  very  soon  after  the  root  emerges,  the  conical  fold  of  the 
leaves  emerges  from  the  other  end  of  the  groove.  This  conical 
form  of  the  folded  leaves  wedges  its  way  directly  upward  through 
the  soil.  The  leaves  elongate  and  unfold. 

THE  PINE. 

13.  The  pine  seed. — The  seeds  of  the  pine  are  formed  on 
the  upper  (inner)  surface  of  the  scales  of  the  pine  cone  (see 
paragraph  529  on  cones  of  the  pine).  The  seeds 
are  oval  and  somewhat  compressed  and  flattened, 
sc  and  attached  to  the  lower  end  of  the  scale,  two 
on  each  scale.  As  they  become  freed  from  the 
.end  scale  a  long,  thin  and  broad  strip  of  the  scale 
splits  off  and  remains  attached  to  the  seed  as 
a  wing.  A  section  of  the  seed  shows  the  thin 
'section  PaPerv  remnant  of  the  nucellus  lying  between  the 
of.  sc.  seed  coat;  n,  see(j  coats  and  the  white  mass  of  the  endosperm. 

remains  of  nucellus; 

end.  endosperm  (=  Within  this  lies  the  embryo.     The  root  and  stern 

female  gametophyte);  ' 

form    a 


cylindri- 

Pnyte-       .  cal    portion,    and 

at  the  stem  end  there  is  a  crown 
of  small  needlelike  leaves,  the  seed 
leaves  or  cotyledons.  The  cotyle- 
dons are  numerous  in  the  pines. 
The  embryo  is  entirely  destitute  of 

,  j  •  .      . 

chlorophyll,  but   during  germma-    Embryo  of  white 

tion,  even  if  the  seedlings  are  grown  £StJ£S£JS2 

in   the   dark    the   leaves   become  cotyledons. 

green.     In  germination  the  radicle  emerges  from  the  micropylar 

end  of  the  seed.     The  hypocotyl  elongates  and  forms  a  loop  which 

pulls  the  leafy  end  of  the  stem  and  the  cotyledons  from  the  ground. 


Fig.  19. 


9* 

Fig.  20. 

Pine  seedling  just 
from    the 


PARTS  OF  SEEDS:   CONCLUSIONS 


II 


CONCLUSIONS 

14.  The  seed. — A  seed  is  a  plant  structure  composed  of  the 
embryo  plant  surrounded  by  the  seed  coats.     The  seed  coats  are 
formed  from  the  walls  of  the  ovule.     The  seed  is 

capable,  by  the  growth  of  the  embryo,  of  produc- 
ing a  plant  similar  to  the  parent. 

The  embryo  is  made  up  of  the  three  principal 
parts  of  the  plant,  the  root,  stem  and  leaf,  but 
these    parts    are    in    a 
very  rudimentary  form. 
Squash,  pea,  bean,  castor 
bean   and    apple   seeds 
are  examples  of  clearly 
denned     seeds.       The 
"  shell  "   of  the  squash 
or   apple    seed    or    the 
membrane    which    can 
be    slipped   off  from  a 
pea  or  bean  after  being  thor- 
oughly   soaked    in    water,    is 
made  up  of   the  seed   coats. 
The    entire    content    of    the 
squash  or  almond  seed  is  the 
embryo. 

15.  Food   stored   in    the 
seed. — Nearly  all  seeds  have 
food  stored  in  them  to  furnish 

nutriment  for  the  embryo  plant  Fig.  21. 

from  the  time  of  germination  White-pine  seedling  casting  seed  coats' 
until  the  seedling  has  established  itself  in  the  earth,  where  it  can 
obtain  its  food  from  the  outside.  In  the  squash,  bean,  pea,  etc., 
the  food  is  stored  up  in  the  two  first  seed  leaves  (cotyledons) 
which  make  the  bulk  of  the  embryo  and  are  easily  recognized 
as  the  two  fleshy  halves.  In  other  seeds,  as  in  the  castor  bean, 
the  corn,  wheat,  etc.,  the  food  is  stored  around,  or  at  one  side  of 


12  GROWTH  AND    WORK  OF   PLANTS 

the  embryo,  within  the  seed  coats,  and  is  then  known  as  endosperm 
(literally  the  inside  of  the  seed). 

16.  Conditions  of  germination  of  seeds. — In  order  that  the 
seeds  of  plants  may  germinate,  certain  conditions  must  be  fulfilled. 
First,  the  seed  must  be  good;  i.e.,  it  must  meet  certain  internal 
conditions,  as  to  maturity,  age,  and  the  vitality  of  the  embryo. 
Second,  the  external  conditions  must  be  favorable.  Seeds  vary 
a  great  deal  as  to  their  viability  according  to  age,  etc. ;  some  seeds 
must  first  pass  a  resting  period  of  several  weeks  or  months  before 
they  will  germinate.  For  most  seeds  there  are  three  external 
conditions  which  must  be  present  in  order  that  they  may  germi- 
nate; air,  a  suitable  amount  of  moisture,  and  a  suitable  degree  of 
warmth.  In  the  absence  of  these  conditions  the  seeds  remain 
dormant  for  a  period  of  time  ranging  from  a  very  few  days  in  the 
case  of  some  kinds  to  many  years  in  the  case  of  others.  If  the  seed 
is  dry  it  will  resist  great  extremes  of  cold  (many  degrees  below 
freezing)  and  warmth.  If  the  seed  is  moist  it  will  resist  these 
extremes  for  a  shorter  period.  Extreme  cold  prevents  or  retards 
germination  of  the  seed.  Growth  begins  slowly  at  about  6°  C. 
(about  43°  F.),  and  increases  with  the  elevation  of  the  tempera- 
ture up  to  an  optimum,  which  is  often  different  in  different  plants, 
and  then  decreases  with  higher  temperatures  until  at  a  maxi- 
mum temperature  growth  ceases.  Germination  may  begin  in  the 
absence  of  air  (of  oxygen)  but  soon  ceases.* 

*  In  the  practical  work  exercises  can  be  arranged  to  demonstrate  the 
influence  of  these  conditions  on  germination. 


CHAPTER   II. 


cot 


NATURE   OF   FOOD  STORED    IN   SEEDS   AND  OTHER 
PLANT   PARTS.* 

17.  In  the  study  of  the  parts  of  the  seed  it  was  found  that 
the  seedlings  are  able  to  make  considerable  growth  when  not 
supplied  with  food  from  the  outside.  This 
growth  goes  on  at  the  expense  of  food  stored 
in  the  seed.  This  food  was  stored  up  in  the 
seed  during  its  formation  in  the  ripening  of 
the  fruit.  In  some  seeds  it  is  laid  down  out- 
side of  the  embryo  and  is  called  endosperm, 
as  in  the  grain  of  corn,  wrheat,  castor  bean, 
etc.  In  others,  while  it  was  first  formed  as 
endosperm  in  the  young  seed,  it  was  largely 
or  completely  absorbed  by  the  embryo  during 
the  ripening  of  the  seed,  as  in  the  bean,  pea,  Fis- *2- 

Section  through  grain  of 

squash,  sunflower,  etc.,  where  it  is  stored  in   com.    s.c.  seed  coats;  st. 

starch,    the   aleurone   layer 

the   Cotyledons  Of   the  embryo.       In  the  Study     Hes  between  the  starch  and 

seed   coats;    cot.    cotyledon 

of    the    seeds   we    have   found   the   general    (here  the  scuteiium)-  >.  rad- 

icle   enclosed   root   sheath; 

location  of  the   food  substance.     We  wish  pi-  plumule, 
now  to  learn  more  particularly  the  form  in  which  it  is  stored,  its 
nature,  as  well  as  the  special  receptacles  and  their  arrangement. 
The  special  receptacles  are  the  cells^  of  the  endosperm,  the  coty- 
ledons, etc.,  where  the  food  is  stored. 

*  It  will  probably  be  found  convenient  to  study  the  nature  and  location 
of  food  substances  while  the  student  is  studying  the  various  seeds,  bulbs, 
shoots,  roots,  etc.,  but  this  short  chapter  is  introduced  here  in  order  to 
avoid  the  unnecessary  description  of  them  with  each  different  object 
studied. 

f  A  cell  is  a  unit  of  microscopic  structure  in  plants.  It  is  like  a  minute 
box  with  cellulose  for  its  walls.  Living  and  growing  cells  contain  the  life 
substance  (protoplasm)  which  has  a  complicated  structure.  In  some  plants 

13 


14  GROWTH  AND    WORK   OF   PLANTS 

18.  Minute  structure  of  the  coats  and  outer  layer  of  food 
reservoir  in  corn  and  wheat  grains. — This  structure  is  deter- 
mined by  a  study  of  a  thin  section  cut  from  a  grain  and  extending 
through  the  outer  surface  and  a  short  distance  into  the  interior  or 
flour  part,  and  magnified  by  the  use  of  the  microscope.  Figure  23 


'o 
Fig.  23. 

Section  through  exterior  part  of  a  grain  of  wheat,  c,  cuticle,  or  outer  layer,  of  bran;  ep,  epi- 
dermis; m,  middle  layer;  i,  it,  layers  of  hull  next  to  seed  coats;  s,  Si,  seed  coats;  p,  layer 
containing  proteid  grains;  st,  cells  of  the  endosperm  filled  with  starch.  Greatly  magnified. 
—  After  Tschirch. 

is  from  a  wheat  grain,  and  the  parts  are  as  follows:  the  outer  layer 
of  cells  (ep)  is  the  epidermis,  and  upon  this  is  the  cuticle  (c);  next 
are  a  few  layers  of  cells  (m)  the  middle  layer  of  brown,  and  next 
(i,  it)  comes  the  inner  layer  of  brown.*  Together  these  are  some- 

the  protoplasmic  units  are  not  bounded  off  by  cell  walls,  still  in  general  we 
can  say  that  the  cell  is  the  unit  of  structure,  at  least  of  the  tissues  of  the 
higher  plants.  A  tissue  is  a  group  of  cells  of  one  kind,  or  in  some  cases  of 
different  kinds  united  together. 

*  These  three  portions  of  the  brown  layers  are  not  a  part  of  the  seed. 
They  are  a  part  of  the  fruit  and  are  in  reality  the  wall  of  the  ovary  inside  of 
which  the  seed  is  formed.  If  this  brown  layer  could  be  entirely  removed 
from  the  grain  of  corn  and  wheat  the  remaining  part  of  the  grain  would  be 
the  seed.  While  then  we  speak  of  the  grain  of  corn  and  wheat  as  seeds  we 
should  remember  that  this  usage  is  not  technically  correct,  for  the  walls  of 
the  seed  capsule  are  consolidated  with  those  of  the  seed. 


NATURE   OF   FOOD  STORED    IN  SEEDS  15 

times  called  the  bran  layer.  The  two  layers  of  cells  (s,  st)  are  the 
two  seed  coats  (the  outer  and  the  inner  seed  coats.  See  the  for- 
mation of  the  seed,  paragraph  305.)  At  p  is  the  aleurone  layer, 
the  cells  containing  proteid  grains,  and  at  st  are  the  starch  con- 
taining cells. 

19.  The  aleurone  layer.  —  Lying  just  within  the  seed  coats  is 
a  single  layer  of  very  regular  cells  rectangular  in  outline  and  nearly 
cuboidal  in  form.     They  are  packed  with  fine  granular  content. 
This  layer  of  cells  is  the  aleurone  layer.     The  granules  in  the 
cells  are  proteid  grains  or  aleurone  grains.     These  proteids  form 
one  of  the  food  substances  stored  in  many  seeds.     The  aleurone 
layer  is  rich  in  nitrogenous  food,   the  proteids  being  a  nitro- 
genous substance  containing  nitrogen   (N),  carbon   (C),  hydro- 
gen  (H),  oxygen  (O),  sulphur  (S)  and  sometimes  phosphorus 
(P).     This  forms  the  most  nutritious  part  of  the  flour,  and  it  is 
well  known  that  nitrogenous  foods,  both  for  plants  and  animals, 
are  much  less  abundant  and  more  costly  than  most  other  foods. 
These  proteids  are  in  composition  very  much  like  the  albumen, 
or  white  of  egg. 

20.  The  starch  in  the  endosperm. — Just  inside  of  the  aleu- 
rone layer  is  a  tissue  of  large   angular  cells  filled  with  coarse 
whitish  grains.     These  are  starch  grains.     Starch  does  not  con- 
tain nitrogen.     It  consists  of  three  elements,   C,   H,   and   O.* 
The  starch  grains  vary  greatly  in  size,  and  in  some  plants  they 
are  much  larger  than  in  others.     If  the  section  of  a  grain  of 
wheat  or  corn  is  treated  with  iodine  the  starch  is  stained  blue 
while  the  aleurone  layer  is  stained  brownish  yellow. 

21.  Starch. — Starch  is  stored  in  plants  usually  in  the  form 
of   grains  which    are   deposited   inside   the   cells.     While   these 
grains  are  microscopic  in  size,  they  vary  a  great  deal  in  different 
plants.     Commercial  starch,  while  it  will  give  the  reactions  for 
starch,  is  not  suitable  for  the  study  of  the  grains,  since  they  are 
destroyed  in  its  preparation.     Starch    becomes   blue    by   treat- 
ment with  a  few  drops  of  a  tincture  of  iodine,  or,  better,  a  solu- 
tion of  iodine  in  potassium  iodide.     Sometimes  the  color  is  more 

*  C8H1006. 


i6 


GROWTH   AND    WORK   OF   PLANTS 


or  less  of  a  purple  or  violet  shade.  We  should  distinguish  be- 
tween reserve  starch  and  transitory  starch.  Reserve  starch  is 
that  which  is  stored  in  special  receptacles  for  future  use  and  is 
that  which  is  utilized  by  man  for  commercial  purposes.  Transi- 
tory starch  is  that  which  is  formed  during  the  day,  and  at  night 
is  transported  to  the  reserve  organs.  Reserve  starch  grains  are 
usually  much  larger  than  transitory  starch  grains. 


Fig.  24. 

A  .   Photomicrograph  of  starch  grainy  B.  Photomicrograph  of  starch  grains 

from  potato.  from  potato,  polarized  light. 

22.  Form  and  appearance  of  starch  grains. — In  the  potato 
tuber  the  starch  grains  are  packed  in  the  cells.  The  grains  are 
of  quite  large  size  as  compared  with  many  other  kinds  of  starch. 
They  present  a  very  interesting  and  characteristic  structure. 
The  grain  appears  to  be  stratified,  the  strata  often  being  in  excen- 
tric  layers.  In  potato  starch  these  strata  are  usually  in  excentric 
rings  about  a  single  spot  called  the  hilum.  These  layers  are 
supposed  to  be  made  up  of  alternate  dense  and  less  dense  layers 
of  the  substance.  Potato  starch  grains  are  oval  to  rhombic  in 
form.  Starch  grains  of  the  corn  are  more  or  less  angular  and  are 
much  smaller  than  those  of  the  potato.  Those  of  the  bean  and 
other  legumes  are  more  or  less  kidney  shaped.  In  the  corn  and 
bean  starch  grains  there  are  often  radiating  lines  from  the  hilum, 


MATURE   OF   FOOD   STORED   IN   SEEDS 


which  aph   ir  like  fissures.    The  starch  grains  of  wheat  are  of  two 
kinds,  very  small  ones,  and  quite  large  ones  mixed  in  with  them. 

33.  The  starch  grains  are  surrounded  by  a  thin  coating  of 
cellulose,  a  substance  similar  to  that  of  which  the  cell  walls  of 
plants  are  made.  This  must  be  dissolved  before  the  plant  can 
use  the  starch  for  food.  The  plant  dissolves  it  by  the  use  of 
certain  cellulose  ferments  manufactured  by  it,  and  then  the  starch 
is  dissolved  by  the  diastase  ferment  (paragraph  180).  A  similar 
diastase  is  present  in  the  saliva  of  man,  but  this  will  not  act  on 
the  starch  grains  unless  the  cellulose  coat  is  broken,  or  dissolved 
by  some  ferment.  Heat  causes  the  starch  grains  to  swell.  If 
they  are  mixed  with  water,  gentle  heat  changes  the  grains  to  a 
paste.  If  dry,  the  cellulose 
coat  is  ruptured  as  the  starch 
swells.  Thorough  cooking 
of  starchy  vegetables  and 
fruits  makes  them  easier  of 
digestion. 

24.  Corrosion  of  starch 
grains  during  germina- 
tion.—  Since  plants  cannot 
absorb  solid  particles  of  food, 
the  embryo  in  the  seed  can- 
not use  the  starch  for  food 
until  after  it  is  dissolved. 
The  embryo  has  the  power 
to  excrete  a  juice  or  ferment 
(diastase)  which  acts  on  the 
starch  grains,  dissolving  them 
and  changing  them  to  a 

-P.                ,,  .  Cell  of  endosperm    of  Indian  corn,  containing 

SUgar.       During   thlS    process  polygonal  starch  grains,  separated  by  thin  plates  of 

,                .           i  protoplasm.    In  the  figures  a  to  g,  the  starch  grains, 

the      Starch      grains      become  taken  from  a  germinating  Indian  corn  grain,  are 

,     ,         m                ^  becoming  dissolved  and  disintegrated. — After  Sachs. 

corroded.     To  see  the  cor- 
roded starch  grains,  take  some  of  the  endosperm  of  the  grain 
of  corn  at  different  stages  of  germination  and  examine  under 
the  microscope.     In  comparing  the   appearance  of  these  starch 


Fig.  25. 


i8 


GROWTH   AND   WORK   OF   PLANTS 


grains  with  those  in  ungerminated  seeds,  the  results  of  the  cor- 
rosion are  clearly  seen. 

25.  Sugar. — Sugar  is  a  substance  closely  related  to  starch. 
Commercial  sugar  is  usually  in  the  form  of  crystals,  or  when 
liquid  it  is  known  as  syrup  or  molasses.     In  the  plant  it  occurs 
in  the  liquid  form  since  it  is  dissolved  in  a  quantity  of  water. 

If  it  were  thick  like  molasses, 
or  in  the  form  of  crystals  like 
commercial  sugar,  it  would 
be  so  strong  as  to  kill  the 
plants  because  it  would  draw 
so  much  water,  by  absorp- 
tion, from  the  surrounding 
tissue,  that  the  protoplasm 
would  be  destroyed.  The 
sugars  found  in  plants  are  of 
three  general  kinds:  cane 
sugar  or  sucrose  abundant  in 
sugar  cane,  sugar  beet,  sugar 
maple,  etc.;  fruit  sugar  or 
glucose  found  in  the  fruit 

Fig-  26.  . 

Cells  from  the  cotyledon  of  the  pea  (Pisum  sati-    OI  a  majority  Ot  plants,  and 
•vum).    st.  starch  grains  with  nucleus  and  concentric        i          j 

stride;    a,   granules  of   aleurone;   *,  i,    intercellular     abundant     in     Some,      aS     in 
spaces.  —  Alter  Sachs.  i 

apples,    pears,  grapes,   etc., 

(in  many  fruits  and  other  parts  of  plants  both  glucose  and  cane 
sugar  are  present) ;  and  malt  sugar  or  maltose,  as  in  malted  barley. 

26.  The  presence  of  grape  sugar  can  be  determined  by  add- 
ing a  solution  of  the  substance  to  "  Fehling's  solution."     Grape 
sugar  "  reduces  "  Fehling's  solution.     It  causes  the  precipitation 
of  copper  and  cuprous  oxide,  a  reddish  substance.     The  presence 
of  cane  sugar  can  be  determined  by  adding  a  solution  of  cobaltous 
nitrate  (5  grains  cobalt  nitrate  in  100  cc.  distilled  water)  to  a  solu- 
tion containing  the  cane  sugar,  followed  by  the  addition  of  a  strong 
sodium  hydrate  solution.    A  beautiful  violet  color  appears.    Grape 
sugar  treated  in  the  same  way  gives  a  blue  color  which  gradually 
changes  to  green.     Cane  sugar  can  be  changed  to  grape  sugar  (or 


NATURE   OF  FOOD   STORED   IN  SEEDS  19 

invert  sugar,  as  it  is  sometimes  called)  by  adding  a  few  drops  of 
strong  hydrochloric  acid  to  a  solution  of  cane  sugar  and  boiling 
for  a  minute  or  two.  By  neutralizing  this  with  sodium  carbonate, 
Fehling's  solution  can  be  used  to  show  that  it  is  grape  sugar.  If 
Fehling's  solution  is  added  to  a  solution  of  cane  sugar,  and  boiled, 
it  will  be  inverted  to  grape  sugar  as  the  red  precipitate  will  show. 
Both  kinds  of  sugar  are  sometimes  found  in  the  same  plant  tissue. 
Both  are  apt  to  be  present  in  the  branches  of  the  sugar  maple  during 
the  autumn,  winter  or  spring. 

27.  Proteids. — Proteids  have  been  mentioned  as  being  present 
in  the  aleurone  layer  of  wheat.     They  also  occur  in  the  seeds 
of  other  cereals.     They  are  present  in  considerable  quantity  in 
beans  and  other  legumes.     They  form  the  principal  food  storage 
in  the  thick  leaves  of  the  onion.     Their  presence  can  be  deter- 
mined by  adding  a  small  quantity  of  strong  nitric  acid  to  portions 
of  the  tissue  and  then  heating.     A  pale  yellow  color  appears. 
If  a  small  quantity  of  ammonium  hydrate  is  now  added  the  color 
is  changed  to  orange. 

28.  Experience  shows  that  several  food  substances  are 
present  in  the  same  object  studied.     For  example,  starch,  sugar 
and  proteids  are  present  in  the  potato  tuber,  but  starch  is  more 
abundant  than  the  other  substances. 

29.  Oil. — Oil  occurs  in  the  tissues  of  various  plants,  but  espe- 
cially in  certain  seeds  as  cotton  seed,  flax  seed,  and  in  many  nuts. 
The  fatty  oils  occur  in  the  form  of  small  translucent  drops  in 
certain  cells.     The  oil  is  obtained  from  seeds  and  nuts  by  sub- 
jecting them  to  great  pressure.     Osmic  acid  blackens  the  oil  and 
its  presence  in  tissue  can  be  detected  by  the  use  of  this  reagent,  or 
by  soaking  pieces  of  the  tissue  in  Flemming's  solution  which  con- 
tains osmic  acid. 

30.  Inulin. — The  food  substance  stored  in  the  roots  of  certain 
composite  plants,  like  the  Jerusalem  artichoke  (Helianthus  tuber- 
osus]  and  the  dahlia,  is  in  solution.     Inulin  is  precipitated  into 
sphaero-crystals  by  prolonged  immersion  of  the  tissue  in  alcohol. 
Many  of  them  are  sometimes  present  in  a  single  cell.     They  show 
peculiar  radiate  and  concentric  markings. 


CHAPTER  III. 


GROWTH  OF  ROOT  AND  STEM. 

31.  Direction  of  growth. — In  studying  the  germination  of 
seeds  one  fact  becomes  very  evident  which  perhaps  was  familiar 
before,  that  the  root  grows  downward  and  the  stem  upward.  This 
is  very  important  for  the  plant  in  order 
that  its  parts  may  establish  a  congenial 
relation  to  their  surroundings,  and  be  in 
a  position  to  perform  their  work;  the  root 
in  the  ground  and  the  foliage  shoot  in  the 
air  and  light.  When  seeds  are  scattered 
by  natural  means  or  are  sown  by  the 
farmer  or  gardener  they  fall  in  various 
positions.  The  seed  may  lie  so  that  the 
embryo  is  upright  and  the  root  already 
pointing  in  a  downward  direction,  or  it 
may  be  horizontal  or  inverted.  Neverthe- 
less, the  root  when  it  emerges  from  the 
seed  turns  downward  to  enter  the  soil,  and 
the  stem  turns  upward.  Some  seeds  which 
are  carried  by  the  wind  are  so  balanced 
that  the  root  end  of  the  embryo  hangs 
downward  (many  composites,  the  clematis, 
etc.,  see  chapter  on  seed  distribution). 

32.  Region  of  elongation  in  roots. 
-The    region    where    elongation    takes 
Pumpkin  seedlings,  the  root   place  in  roots  is  determined  by  a  careful 

marked  in  left.  Right  one  show-        ,        .  r      ,  .    ,  i_  r 

ing  where  growth  took  place  in     plotting    OI     the     TOOt     into     a     number     OI 
twenty-four  hours.  .  i   i        i  •          .  i  j 

small  sections,  and  by  keeping  the  seed- 
ling in  an  upright  position  in  moist  air.  Subsequent  observa- 
tions and  a  careful  plotting  of  the  root  from  day  to  day  shows 

20 


GROWTH   OF   ROOT   AND   STEM 


21 


that  the  elongating  part  of  the  root  occupies  a  certain  area  back 
of  the  tip.  This  elongation  is  due  to  the  elongation  of  individual 
cells  which  are  constantly  being  formed  in  the  growing  point  of 
the  tip,  and  are  left  behind.  These  cells  elongate  slowly  at  first, 
then  rapidly  and  then  slowly  again  until  they  cease  to  elongate. 
All  of  the  cells  in  one  cross  area  of  the  root  grow  at  about  the  same 
rate  at  the  same  time.  Their  united  action  then  is  manifest  in 
the  slow  elongation  of  the  root  just  back  of  the  tip,  its  more  rapid 
elongation  further  back,  followed  by  the  slow  elongation  again 
until  elongation  finally  ceases. 

33.  Region  of  elongation  in  stems. — The  region  of  elonga- 
tion in  stems  is  determined  in  a  similar  way.     It  occurs  just  back 
of  the  growing  point,  but  covers  usually  a  greater  area  than  in  the 
root. 

34.  The  motor  zone  in  roots,  or  region  of  curvature. — 
After  a  seedling  or  a  plant  has  been  growing  in  one  direction  for 
a  time,  if  its  position  be  changed  so  that  the  root  and  stem  are  in 
a  horizontal  position,  or 

at  any  angle  from  the  up- 
right, the  root  and  stem 
will  curve  so  that  the  root 
grows  downward  and  the 
stem  upward.  The  region 
of  curvature  of  the  root 
under  these  circumstances 
corresponds  with  the  re- 
gion of  elongation.  This 
curvature  is  made  possible 
because  the  cells  in  the 
region  of  the  root  are  all 
elongating.  Those  on  the  upper  side  of  the  root  elongate  more 
than  those  on  the  underside  and  bring  about  the  curvature. 

35.  The  perceptive  zone  in  roots. — The  perceptive  zone  in 
roots  is  that  part  of  the  root  which  receives  the  stimulus  causing 
it  to  turn  downward.     It  is,  therefore,  a  sense  organ. 

The  stimulus  which  causes  the  root  to  turn  downward  is  initiated 


Fig.  28. 

Bean  seedling  placed  horizontally  and  marked  to 
show  where  the  root  bends. 


22  GROWTH   AND   WORK   OF   PLANTS 

by  gravity.  We  must  be  careful,  however,  not  to  confuse  this 
stimulus  from  gravity  with  the  pull  which  gravity  exerts  on  all 
bodies.  For  example,  if  we  lift  a  seedling  and  then  "  let  go  "  of 
it,  it  will  fall  to  the  ground,  or  until  it  meets  some  object  which 
intercepts  it.  It  is  not  this  force  of  gravity  which  causes  the  roots 
of  plants  to  grow  in  a  downward  direction.  Gravity  merely  in- 
itiates a  stimulus  in  response  to  which  the  root  turns  downward. 
It  has  been  found  that  this  perceptive  zone,  which  perceives  the 
stimulus,  is  in  the  root  tip.  While  the  root  tip  receives  the  stimu- 
lus, this  is  not  the  part  of  the  root  which  curves.  The  curvature 
takes  place  in  the  motor  zone,  or  region  of  growth  by  elongation. 
The  stimulus  received  by  the  sense  organ  in  the  root  tip  is  carried 
back  to  the  growth  region,  and  the  cells  on  the  upper  side  of  the 
horizontal  root  elongate  faster  than  those  on  the  under  side,  and 
the  curving  results. 

36.  How  it  is  determined  that  gravity  stimulates  the  root 
to  grow  in  a  downward  direction. — This  is   shown   by  con- 
stantly changing  the  position  of  the  root,  so  that  the  stimulating 
influence  of  gravity  is  neutralized  and  does  not  act  for  a  long 
enough  time  in  one  direction  upon  the  sense  organ  in  the  root  tip 
to  accumulate  a  sufficient  amount  of  excitation  from  the  stimu- 
lus.    This  is  done  by  pinning  seedlings  in  various  positions  upon 
an  upright   revolving   disk   or  wheel.     The   wheel   is   revolved 
slowly,  and  dripping  water  is  used  to  keep  the  roots  moist.     The 
roots  and  stems  will  continue  to  elongate  in  the  same  direction 
in  which  they  were  placed.     The  wheel  can  be  revolved  by  a  slow 
small  stream  of  water  from  the  hydrant,  or  by  clock  arrange- 
ment. 

37.  Geotropism. — The   direction   of    growth   of    stems    and 
roots,  when  uninfluenced  by  light,   as  shown  in  the  preceding 
paragraphs,   is  caused  by  the   stimulus  from  the   influence   of 
gravity.     This  stimulus  causes  a  turning  of  the  stem  or  root  in  a 
definite  direction  in  relation  to  the  earth.     This  phenomenon  is 
called,  therefore,  geotropism,  which  name  means  literally  earth 
turning,  since  the  earth  in  this  case  is  the  body  which  provides 
the  gravitation  influence.     The  turning  of  the  root  towards  the 


GROWTH   OF   ROOT  AND   STEM 


earth  is  positive  geotropism,  or  progeotropism.  The  turning  of 
the  stem  away  from  the  earth  is  negative  geotropism,  or  apogeo- 
tropism.  The  primary  root  is 
therefore  progeotropic,  the  pri- 
mary stem  is  apogeotropic. 
Lateral  roots  show  transverse 
geotropism,  or  dia geotropism, 
since  their  direction  of  growth 
is  sideways  or  lateral. 

38.  Change  in  the  direc- 
tion of  growth  of  lateral 
branches. —  This  takes  place 
when  the  main  shoot  or 
"leader"  is  destroyed  or  re- 
moved. One  or  more  branches 
change  from  growth  in  a  lat- 
eral direction  to  an  upright 

Fig.  29. 


Pea  seedling ;  lateral  roots  turning  downward 
after  primary  root  has  been  cut  off. 


direction.  This  is  very  strik- 
ing in  certain  trees  like  some 
conifers  (pines,  spruces,  etc.). 
When  the  top  of  a  young  pine  is  cut  off  one  or  two  of  the  lateral 
branches  gradually  curve  upward  and  take  the  place  of  the 
leader.  This  is  sometimes  very  common  in  the  white  pine  where 
the  larva  of  a  beetle  kills  the  top  of  the  main  shoot  or  leader. 
Pine  or  spruce  trees  struck  by  lightning  in  such  a  way  that  a 
large  part  of  the  top  is  broken  off,  present  a  few  years  later  a 
very  singular  appearance,  the  topmost  lateral  branches  remain- 
ing spread  out  for  some  distance.  They  are  too  old  and  firm  for 
one  or  two  of  them  to  turn  upward  and  take  the  place  of  the 
"  leader."  But  a  number  of  small  branchlets  on  the  upper  sur- 
face of  several  of  these  lateral  branches  grow  directly  upward 
making  a  small  forest  or  grove  of  trees  in  the  top  of  a  single 
tree. 

39.  Work  performed  by  roots  in  penetrating  the  soil. — 
One  of  the  important  kinds  of  work  which  the  roots  perform  is 
the  penetration  of  the  soil  or  substratum  where  the  plant  is 


GROWTH  AND   WORK   OF   PLANTS 


growing.  Even  where  the  soil  is  quite  hard  and  compact  we 
often  find  it  permeated  with  a  perfect  maze  of  delicate  roots. 
The  action  of  the  root  in  penetrating  the  soil  is  much  like  that  of 
a  wedge,  except  that  the  driving  force  is  different,  and  the  for- 
ward movement  of  the  root 
lies  in  a  short  section  just 
back  of  the  tip  which  is 
constantly  shifting  from  old 
cells  to  new  ones.  The 
driving  force  for  forward 
movement  in  the  root  comes 
from  the  growth  of  the  cells 
in  the  zone  of  elongation, 
while  the  widening  force 
comes  mainly  from  growth 
in  thickness.  Since  the 

Fig  30  driving  force  comes  from 

elongation  of  cells  near  the 
tip  of  the  root,  the  older 
part  of  the  root  must  be  held  in  place,  otherwise  the  root 
would  simply  be  pushed  backward  out  of  the  ground.  If  the 
seed  germinated  when  on  the  surface  of  the  ground  the  root 
could  not  well  enter.  In  case  of  the  seedling  the  root  hairs  serve 
to  anchor  the  young  root  until  the  lateral  roots  are  formed,  when 
the  young  root  system  as  a  whole  furnishes  the  anchorage.  The 
tip  of  the  root  is  pushed  with  considerable  force  against  the  soil 
particles  in  advance,  and  being  conical  in  form  turns  them  to  one 
side.  The  rigidity  of  the  older  parts  of  the  young  root,  as  well 
as  the  wall  of  earth  around  it,  prevents  the  root  from  bending. 

40.  Force  exerted  by  growth. — The  force  exerted  by  roots 
and  stems  as  a  result  of  growth  is  remarkable.  Even  in  the  case 
of  young  seedlings  the  hard  crust  of  the  soil  is  often  broken  as 
the  stem  rises.  In  rocky  places  it  is  a  common  thing  to  see  small 
crevices  in  rocks,  where  the  slender  roots  of  trees  enter,  broaden, 
and  the  rock  is  split  apart  as  the  root  enlarges.  The  force  exerted 
by  such  delicate  plants  as  mushrooms  is  seen  where  they  burst 


Roots  of  peas  entering  soil  after  anchorage  by  root 
hair. 


GROWTH   OF   ROOT   AND   STEM  2$ 

through  hard  dry  ground.     One  should  improve  the  opportuni- 
ties for  observing  all  such  phenomena  when  occasion  offers. 

41 .  Influence  of  light  on  the  direction  of  growth  of  stems 
and  roots. — Besides  the  stimulus  of  gravity  there  is  the  stimu- 
lus of  light  which  influences  the  direction  of  growth  of  stem  and 
root.     Roots  are  mostly  in  the  dark  and  therefore   are  rarely 
influenced  by  light.     When  seedlings  of  certain  plants  are  grown 
in  water  cultures  and  have  a  one-sided   illumination  the  roots 
turn  away  from  the  light,  but  since  geotropism  is  also  acting  on 
them  they  are  turned  obliquely  to  one  side.     In  the  same  way 
when  the  stems  have  come  above  ground  they  are  still  under 
the  influence  of  the  stimulus  of  gravity.     But  the  stimulus  of 
light  is  usually  more  powerful  and  has  more  influence  in  deter- 
mining*the  direction  of  growth  of  the  stem  and  its  branches.     Light 
thus  has  a  very  important  influence  in  determining  the  form  of 
the  stem.     The  stimulus  of  light  causes  the  stem  to  turn  toward 
the  light. 

42.  Heliotropism. — The  turning   of   plant   parts   under  the 
influence  of  light  is  called  heliotropism,  a  turning  toward  the  sun, 
or  light,  or  more  properly  speaking,  a  turning  influenced  by  the 
stimulus  of  light.     Heliotropism  then  is  the  name  -given  to  the 
phenomenon  in  its  broadest  sense.     Positive  heliotropism  or  pro- 
heliotropism  is  a  turning  toward  the  light;    negative  heliotropism 
or  apoheliotropism  is  a  turning  away  from  the  light;    and  trans- 
verse heliotropism  or  diaheliotropism  is  a  lateral  turning  under 
the  influence  of  light. 


CHAPTER   IV. 

ROOTS,   THEIR  KINDS,    MECHANICAL  WORK   AND 
STRUCTURE. 

43.  There  are  two  kinds  of  work  which  nearly  all  roots  per- 
form:   First,  the  absorption  of  water  and  food  solutions;   second, 

that  of  attachment  and  support  for 
the  plant.  In  addition  there  are  cases 
where  roots  of  certain  plants  serve 
other  purposes  as  well,  for  example, 
where  they  serve  as  storehouses  for 
food.  In  some  of  these  the  root  takes 
on  a  special  form  which  enables  it 
to  hold  large  reserves  of  food.  Such 
food  reservoirs  are  seen  in  the  sweet 
potato,  the  tuber-rooted  sunflower, 
dahlia,  carrot,  parsnip,  etc.  In  other 
cases  food  materials  are  held  in  re- 
serve during  certain  seasons  in  large 
roots  of  trees,  or  in  roots  of  peren- 
nial or  biennial  plants,  where  they 
are  not  specialized  as  food  reser- 
voirs. 

ROOT   SYSTEM. 

44.  The  root  system  of  a  plant 
includes  all  the  roots  of  a  single  plant, 
but  has  special  reference  to  the  form, 
the   branching  of   the   system   as    a 
whole  determined  by  the  mode,  ex- 
Tap  roots  o^par'snip  and  carrot,  tent,  direction  and  character  of  the 
tu£rsfleshy  °nes  are  als°  called  Cr°wn  branching.     There  are  several  types 

26 


OF    THE  \ 

UNIVERSITY,  J 


ROOTS:   ROOT  SYSTE. 

of  root  systems,  and  these  are  seen  to  be  peculiar  to  certain  plants. 
For  example : 

45.  The  tap-root  system. — Plants  possessing  a  tap-root 
system  are  those  which  have  a  prominent  root  called  the  tap 
root,  which  is  stout  and  extends  downward  to  some  depth  in  the 
soil,  as  in  the  dandelion.  This  is  usually  developed  from  .  the 
primary  root.  There  are  numerous  lateral  roots  but  they  are 
usually  slender.  The  carrot,  parsnip,  etc.,  are  other  examples. 
The  fibrous-root  system  is  very  different.  The  roots  are  com- 
paratively slender-  and  much  branched,  as  in  the  bean,  corn, 
etc.  Fascicled  roots.  Thickened  or  fleshy  roots  developed  in 
clusters  or  fascicles  are  called  fascicled  roots.  A  good  example  is 
seen  in  the  dahlia  with  a  tuft  of  stout  fusiform  roots. 


Fig.  32. 
Fascicled  roots  of  the  dahlia. 

46.  Relation  of  root  system  to  the  soil.— The  relation  of 
the  root  system  of  plants  to  the  soil  is  a  very  important  one,  and 
is  governed  to  some  extent  by  the  nature  of  the  soil,  the  moisture 
content  and  distribution  of  the  plant  food.  Plants  with  a  tap- 
root system  have  an  advantage  over  those  with  a  shallow  fibrous- 
root  system  in  dry  soils  or  in  dry  weather,  since  the  roots  are  able 
to  reach  the  moisture  at  the  lower  levels  in  the  soil.  Evaporation 
removes  the  moisture  from  the  surface  layers  rapidly  in  dry 
soil  and  in  dry  periods,  and  plants  with  a  root  system  developed 
near  the  surface  are  the  first  to  suffer.  Hickory  and  walnut 
trees  have  a  tap  root  which  extends  to  great  depths  in  the  soil, 


28  GROWTH   AND    WORK   OF  PLANTS 

and  have  little  difficulty  in  obtaining  the  necessary  water  in  dry 
soils  or  in  dry  seasons.  Cone-bearing  trees,  the  pines,  spruces, 
etc.,  have  a  shallow  root  system,  and  are  especially  suited  to 
growing  in  regions  where  plant  food  is  chiefly  confined  near  the 
surface  of  the  ground.  Plants  growing  in  the  desert,  except  the 
annuals,  which  grow  only  during  the  rainy  season,  usually  have 
a  root  system  which  extends  to  a  considerable  depth  in  the 
soil. 

47.  The  mesquite  tree  of  the  Southwestern  States  and  Mexico 
is  a  remarkable  example  of  the  relation  of  the  roots  to  the  soil 
under  different  conditions.     Where  the  soil  is  not  very  dry  it 
forms  a  large  tree  and  the  roots  do  not  extend  very  deeply  into 
the  soil.     In  the  very  dry  regions,  however,  the  tree  attains  a 
height  of  only  two  or  three  feet  and  it  extends  its  roots  very 
deeply  into  the  soil,  sixty  feet  or  more,  to  obtain  water. 

KINDS   OF   ROOTS. 

Besides  the  variation  in  the  root  system  of  plants,  there  are 
several  kinds  of  roots  which  do  special  work  for  the  plant. 

48.  Aerial  roots. — These  are  most  common  in  the  case  of 
many  tropical   plants  which   grow   on  trees.     Such   plants   are 
epiphytes.     The  roots  here  serve  as  grapplers  to  attach  the  plants 


Fig.  33- 
Aerial  roots  of  wandering  Jew  (Tradescantia). 


to  the  limbs  and  trunks  of  trees.  Good  examples  of  these  can  be 
seen  in  the  case  of  many  tropical  orchids  which  are  grown  in  so 
many  greenhouses.  Some  of  the  roots  dangle  in  the  air  and  are 
provided  with  a  special  sheath  of  spongy  tissue  (the  vela  men) 


ROOTS:   KINDS   OF   ROOTS 


29 


which  absorbs  moisture  from  the  air.  Another  example  common 
in  greenhouses  is  the  wandering  Jew  (Tradescantia}.  The 
aerial  roots  grow  from  the  joints,  usually  two  roots  from  each 
joint.  Good  examples  of  aerial  roots  can  be  seen  in  the  case 
of  the  climbing  poison  ivy,  English  ivy,  trumpet  creeper,  etc. 
These  serve  to  hold  the  vine  to  the  tree  or  other  support  on  which 
it  is  climbing. 

49.  Bracing  roots,  or  prop  roots. — In  some  plants  where 
the  fibrous-root  system  in  the  soil  is  not  sufficient  to  support  the 
heavy  plant  upright,  aerial  roots 

are  developed  a  short  distance 
above  the  ground  and  as  they 
reach  the  soil  serve  to  prop  or 
brace  the  plant.  Good  exam- 
ples are  seen  in  the  Indian  corn, 
and  in  the  screw  pine  grown  so 
commonly  in  greenhouses.  A 
classic  example  of  prop  roots 
is  seen  in  the  banyan  tree  of 
India  where  numerous  roots 
grow  downward  from  the  wide 
spreading  branches.  The  man- 
grove along  the  coast  in  the  subtropical  regions  of  Florida  is 
another  example. 

50.  Strangling  roots. — In  some  tropical  countries  there  are 
trees  (Clusia)  which  begin  their  life  as  seedlings  on  other  trees 
from  seeds  which  have  lodged  in  the  fork  of  a  branch  or  some 
other  landing  place.     Slender  roots  grow  down  to  the  ground,  one 
of  which  forms  this  part  of  the  trunk.     Other  roots  coil  around 
the  foster  tree.     When  the  Clusia  becomes  a  large  tree  these 
roots  wrapped  around  the  foster  tree  tightly  strangle  and  kill  it.* 

51.  Fleshy  roots,  or  root  tubers.— There  are  roots  or  por- 
tions of  roots  which  have  become  large  and   fleshy,  as  in  the 
sweet  potato  or  the  dahlia.     Such  roots  are    reservoirs   where 
plant  food  is  stored  to  be  used  later  by  the  plant  for  growth  or 

*  See  "A  Tragedy  of  the  Forest,"  Torreya  8,  253-259,  1908. 


Fig.  34- 
Bracing  roots  of  Indian  corn 


30  GROWTH   AND    WORK   OF   PLANTS 

seed  production  or  for  starting  new  plants.  In  the  sweet  potato 
the  food  is  stored  as  sugar,  while  in  the  dahlia  it  is  stored  as 
inulin,  common  in  many  composites.  In  the  natural  condition 
it  is  in  solution,  but  by  prolonged  immersion  of  the  tissue  in 
alcohol  the  inulin  is  precipitated  in  the  form  of  sphaero  crystals. 

52.  External  structure  near  and  including  the  root  tip.— 
The  principal  general  features  in  the  structure  of  roots  can  be 
obtained  in  the  study  of  the  roots  of  seedlings.  The  form  of  the 
extreme  tip  is  conic,  and  it  consists  of  a  group  of  cells  which  are 
loosely  held  together,  especially  on  the  outer  surface,  where 
they  constantly  become  free  and  die.  This  is  the  root  cap,  and 
it  protects  the  delicate  growing  cells  just  back  of  the  tip.  A 
splendid  example  of  the  root  cap  is  afforded  by  the  screw  pine. 
It  is  very  large  and  can  very  readily  be  seen  on  the  prop  roots 
before  they  reach  the  soil.  Another  interesting  example  is  found 
on  the  roots  of  the  water  hyacinth  common  in  some  of  the  streams 
of  Florida  and  sometimes  grown  in  aquaria  in  greenhouses.  The 
root  cap  is  long  and  can  be  very  easily  pulled  from  the  root  and 

then  slipped  on  again.  Just  back 
of  these  loose  cells  and  still  near 
the  tip,  the  surface  of  the  root  is 
smooth  and  the  cells  are  united 
closely  and  firmly.  The  outer  layer 
of  cells,  somewhat  elongated  and 
rectangular,  forms  the  "skin"  or 
epidermis  as  it  is  more  properly 
called.  When  the  young  root  is 
transparent  this  layer  can  be  traced 
some  distance  underneath  the  root 
cap  where  it  arises  from  the  meri- 
Fig.  35-  stem  (see  paragraph  54),  and  the 

Germinating  wheat,  showing  root  hairs.    ^.^    Qf    ^    ^^    ^^   ^ 

also  be  seen  (fig.  37).  A  little  farther  back  from  the  tip  of  the 
root  some  of  the  epidermal  cells  grow  out  into  the  long  root 
hairs.  The  root  hairs  occupy  a  rather  definite  area  of  the  root 
a  little  distance  back  from  the  tip.  As  the  root  elongates  new 


ROOTS:  KINDS  OF  ROOTS  31 

root  hairs  are  constantly  being  developed  from  newly  formed 
epidermal  cells,  while  all  the  older  root  hairs  behind  are  con- 
stantly dying  and  disappearing.  They  are  long,  slender,  tubular 
cells,  and  since  they  serve  the  important  purpose  of  absorbing 
water  and  mineral  food  solutions  from  the  soil,  they  must  be  fresh 
and  new. 

53.  Internal  structure  of  the  root. — Fig.  36  represents  a  cross 
section  of  a  root.  The  outer  layer  of  cells  is  the  epidermis  from 
which  the  root  hairs  arise.  Just 
inside  of  the  epidermis  is  the 
cortex,  which  consists  of  several 
layers  of  cells  more  or  less  rounded 
and  with  air  spaces  between  where 
they  touch  adjacent  cells.  Inside 
of  this  is  a  ring  of  a  single  layer 
of  rather  thin  cells  (the  pericycle}. 
This  can  be  located  by  observing 
that  it  lies  just  outside  of  groups 
of  cells  so  highly  differentiated  in 

the  Center.      These  groups  of  Cells,        Section  of  corn  root,  showing  root  hairs 
.LI.  -xu    j.u      xU'  11    j  r  formed  from  elongated  epidermal  cells. 

together  with  the  thin-walled  fun- 

damehtal  cells  which  are  between  them,  make  the  central  cylinder 
(fig.  37).  There  are  often  eight  groups  of  special  cells  seen  in  cross 
section  of  a  young  root.  Four  of  these,  the  more  prominent 
ones,  are  the  fibre-vascular  bundles  (paragraph  98).  They  are 
broad  inward  and  narrowed  outward  as  seen  in  cross  section. 
The  larger  cells  are  the  vessels  or  tubes  through  which  the  water 
or  "  sap  "  flows  in  the  root.  Besides  the  vessels  there  are  thick- 
walled  wood  fibers,  and  on  the  outer  side  also  some  young  thin- 
walled  living  cells  which  divide  and  grow  to  form  additional  cells 
for  the  bundle  as  the  root  increases  in  diameter.  The  tissue  of 
these  bundles  is  woody  and  is  the  xylem  (paragraph  98).  Alter- 
nating with  these  four  radiating  groups  of  wood  cells  are  four  other 
groups  of  bast  cells  (or  phloem),  which  lie  near  the  pericycle.  The 
tissue  of  thin-walled  cells  lying  between  these  groups  is  funda- 
mental tissue,  parenchyma  (paragraph  94). 


GROWTH   AND    WORK  OF   PLANTS 


54.  Origin  of  the  tissues  of  the  root.—  This  can  be  studied 
in  a  longitudinal  section  of  a  young  root  including  the  tip.  The 
epidermis  is  the  outer  layer  of  cells.  Towards  the  root  tip  the 
rows  of  epidermal  cells  converge  on  a  curve  and  meet  near  the 


P'o 


middle  in  a  tissue  of 
cells  rich  in  protoplasm 
and  with  thin  walls  (the 
meristem,  a  group  of 
growing  cells  at  the  end 
of  roots  and  stems).  The 
cortex  lies  just  inside  of 
the  epidermis  and  con- 
sists of  several  rows  of 
cells  on  each  side.  In- 
side of  the  cortex  is 
the  central  cylinder.  By 
consulting  fig.  37  the 
position  and  limits  of 
these  tissues  can  be  seen. 
The  meristem  is  the  tis- 
sue from  which  the  oth- 
ers arise.  Its  cells  divide 
and  the  older  ones  pass 

Lengthwise  section  (somewhat  diagrammatic)  through  .    .  ,    .  .  , 

root  tip  of  Indian  corn,  w,  root  cap;  *,  younger  part  of  baCK  into  epidermis  COr- 
cap;  z,  dead  cells  separating  from  cap;  s,  growing  point;  . 

o,  epidermis;  p't  intermediate  layer  between  epidermis  and  tCX  and  Central  Cylinder. 
central  cylinder;  p,  central  cylinder,  in  which  the  fibro-  ,. 

vascular  bundles  arise.  —  After  Wiesner.  In    the    Central    Cylinder 

there  is  a  great  variety  of  cells.  In  the  meristem  where  these  cells 
arise  they  are  all  alike,  but  as  they  age  and  pass  over  into  the  differ- 
ent tissues  they  take  on  the  special  forms  which  make  them  suit- 
able for  their  special  kind  of  work.  This  is  an  interesting  and 
important  change,  since  economy  and  the  highest  utility  are  gained 
in  this  division  of  labor  and  specialization  among  the  working  cells 
of  the  root.  In  a  similar  way  the  specialized  cells  of  stems,  leaves 
and  flowers  arise  from  a  meristem  of  simple  undifferentiated  cells. 
The  plant  body  may  thus  be  compared  to  a  highly  organized  and 
developed  community  of  individuals,  each  with  its  special  work  to 
do,  and  all  working  together  for  the  common  good. 


CHAPTER  V. 

WORK   OF   ROOTS   IN   ABSORPTION   OF  WATER   AND 
FOOD    FROM   THE    SOIL. 


55.  Absorption  of  water  and  food  sub- 
stances from  the  soil. — Land  plants  absorb 
water  and  food  solutions  chiefly  through  the  root 
hairs.     In  the  study  of  seedlings  we  observed 
the  form  of  the  root  hairs  and  their  position  on 
the  roots.      They  are  very  slender,  long   cells 
developed  in  great  numbers  over  the  surface  of 
the  root  a  little  distance  back  from  the  tip  of 
the  root.     The  root  hairs  are  not  permanent 
as  in  the  case  of  most  of  the  roots.    As  the 
root  elongates,  new  root  hairs  are  formed,  while 
the  older  ones  farther  back  on  the  stem  die. 
Thus  the  root  hairs  are  fresh  and  in  good  con- 
dition for  their  work  of  absorption. 

56.  How    the   root   hairs    absorb  water 
from  the  soil. — Each  root  hair  is  a  plant  cell 
which  is  very  much  elongated.     It  is  formed  by 
the  lateral  elongation  of  one  of  the  cells  of  the 
skin  or  epidermis  of  the  root.     The  outer  part 
or  boundary  of  the  root  hair  is  its  cell  wall.     It 
is  thin  and  white.     Inside  of  the  root  hair  is  a 
granular,  whitish,  slimy  substance.     This  is  the 
living  substance  of  the  cell,  and  is  calleT  proto- 
plasm.    It  is  the  living  protoplasm  in  the  root 
hair  which  enables  it  to  take  up  water  and  food 
solutions. 

There  is  a  thin  and  continuous  membrane  of 


Fig.  38. 


Root  hair  of  corn  before 
,.    ,     , .  and  after  treatment  with 

protoplasm  which  lines  the  wa^_    Inside  of  this  s  per  cent  salt  solution. 

33 


34  GROWTH   AND    WORK  OF   PLANTS 

membrane  the  entire  space  of  the  cell  is  not  filled  with  proto- 
plasm. There  are  large  spaces  filled  with  a  watery  fluid  called 
cell  sap,  which  is  a  solution  of  certain  salts,  sugars,  etc.,  in 
water.  If  the  root  hairs  are  placed  in  a  5  per  cent  salt  solution, 
the  membrane  of  protoplasm  lies  between  the  cell  sap  inside 
of  the  cell  and  the  salt  solution.  The  cell  wall  permits  the  water 
and  solutions  to  filter  through  easily.  Butjthe  protoplasmic 
membrane^is  ofa  closer  and  different  texture,  so__thal_soluble 
substances  do_jiojjas&.  thrmigji  so  readily.  The  water  of  the 
solution,  however,  passes  through  the  membrane  easily.  The 
result  is  that  the  protoplasm  contracts  away  from  the  cell 
wall.  This  is  because  some  of  the  water  in  the  cell  sap  flowed 
through  the  protoplasmic  membrane  into  the  salt  solution  outside. 
According  to  well-known  laws  of  physics,  the  greater  flow  of  water 
through  such  a  membrane,  which  is  only  half-way  permeable 
(semi-permeable),  is  always  in^he  direction  of  the  stronger  solu- 
tion. This  shows  then  that  the  5  per  cent  salt  solution  is  stronger 
than  the  cell-sap  solution.  But  when  the  salt  solution  is  replaced 
with  water,  the  membrane  of  protoplasm  moves  out  again  against 
the  cell  wall  and  is  pressed  firmly  against  it,  so  that  the  elastic  cell 
wall  becomes  slightly  stretched  while  the  cell  becomes  firm  and 
turgid,  or  is  in  a  state  of  turgescence,  or  tension,  something  like  an 
inflated  bladder.  This  action  of  the  protoplasmic  membrane, 
the  cell  wall,  and  the  cell  sap  explains  to  us  how  it  is  that  the  deli- 
cate root  hairs  can  take  up  water  and  food  solutions  from  the  soil. 
57.  The  behavior  of  a  root  hair  or  other  cell  in  the  absorp- 
tion of  water  is  sometimes  illustrated  in  the  following  way.* 
Over  the  bulb  of  a  thistle  tube  a  piece  of  a  bladder  membrane  is 
tied  after  thoroughly  soaking  it.  A  saturated  solution  of  sugar 
in  water  with  a  small  quantity  of  a  red  analine  dye  to  color  it  is 
poured  into  the  tube  to  fill  the  bulb  and  a  short  distance  into  the 
tube.  The  bulb  of  the  thistle  tube  is  lowered  into  a  bottle  of 
water  so  that  the  height  of  the  water  in  the  bottle  and  the  solution 
in  the  tube  are  at  the  same  level.  In  a  few  hours  or  in  a  day  or  so, 
if  the  experiment  is  properly  set  up,  the  solution  in  the  tube  will 
*  Or  by  the  well-known  egg  experiment. 


WORK   OF   ROOTS   IN   ABSORPTION  35 

rise  above  the  surface  of  the  water  in  the  bottle.  Water  then 
flows  through  the  membrane  into  the  sugar  solution,  but  the  sugar 
and  the  dye  do  not  pass  through  the  membrane  to  any  great  extent 
unless  left  for  a  long  time. 

58.  Turgor  in    the  plant   cell  is 
sometimes  illustrated   in  the   following 

way.     A  medium-sized  vial  is  filled  with  'puncturing  an 

a  saturated  solution^!  sugar.    Over  the  jf 

open  end  a  piece  of  bladder  membrane  m  water* 

which  has   been    thoroughly  soaked  is 

securely  tied  in  such  a  way  as  to  exclude       F; 

the  air.     The  vial  is  then  immersed  in      Same  as  Fig. 

39  after  needle 

a  vessel  of  water  and  allowred  to  stand  is  removed. 

for  a  day  or  two.     It  is  then  taken  from 

the  vessel  of  water.     The'  membrane  is  arched  upward  as  if  by 

a  pressure  within.     If  the  membrane  is  pricked  with  a  needle, 

and  the  instrument  quickly  withdrawn,  a  stream  of  water  spurts 

out  because  of  the  inside  pressure. 

59.  How  the  root  hairs  get  water  from   the  soil. — Most 
land  plants  get  their  water  and  food  solutions  from  soil  which  is 
moist  or  sometimes  even  appears  dry.     How  can  they  take  up 
water  from  moist  soil  or  from  soil  which  is  so  dry  that  no  water 
can  be  pumped  from  it?    The  soil  is  composed  of  very  finely 
pulverized  rock,  in  the  form  of  minute  angular  grains.     Mixed 
with  these  fine  grains  is  more  or  less  matter  of  an  prga-ni'r  "^nrpj 
the  disintegrated  remain??  of  plants      When  soil  is  not  saturated 
with  water,  the  water  present  is  in  the  form  of  a  thin  film  wBich 
surrounds  the  soil  particles.     The  soil  particles  touch  each  other, 
but  because  of  their  form  there  are  spaces  between  them  just  as 
there  are  spaces  between  the  stones  in  a  pile.     The  film  of  water 
which  surrounds  the  soil  particles  meets  and  joins  with  adjacent 
soil  particles  at  their  points  of  contact,  thus  making  a  continuous 
film  for  a  great  extent  through  the  soil,  reaching  down  to  the 
ground  water  below.     The  spaces  between  the  soil  particles  are 
filled  with  air,  which  is  very  necessary  for  the  health  of  the  plant. 
The  root  hairs  of  plants  being  attached^very  closely  and  firmly 


36  GROWTH   AND    WORK   OF   PLANTS 

to  some  of  these  soil  particles  are  thus  brought  into  very  close  con- 
tact with  the  water  film  in  the  soil,  and  absorb  it,  while  fresh 
water  is  drawn  through  the  film  from  the  ground  water  below. 
Where  free  soil  water  is  present  in  the  soil  for  any  length  of  time 
about  the  roots  of  most  dry  land  plants,  the  plants  become 
sickly.  Many  plants,  however,  grow  in  soil  where  there  is  free 
soil  water  continually,  or  for  a  great  portion  of  the  time.  Ex- 
amples are  seen  in  the  swamp  plants,  semiaquatics,  etc. 


i 


CHAPTER  VI. 
TYPES  AND  KINDS  OF  STEMS. 

60.  Kinds  of  plants  with  reference  to  the  length  of  their 
life. — There  are  three  kinds  of  plants  as  regards  the  normal 
duration  of  their  life,  annuals,  biennials,  and  perennials.  An 
annual  is  a  plant  which  makes  its  entire  growth  in  one  year  or 
season,  from  the  germination  of  the  seed  to  maturity,  when  new 
seed  is  ripened  and  the  plant  dies.  Some  may  accomplish  this 
in  a  few  weeks,  others  require  the  entire  season  from  early  spring 
to  late  autumn.  There  are  many  examples  of  annuals  among 
our  common  plants,  as  the  corn,  buckwheat,  oats,  morning  glory, 
sunflower,  bean,  peas,  etc.  A  biennial  is  a  plant  which  starts 
from  the  seed  one  season  and  lives  over  to  the  season  of  the 
second  year  before  the  ripening  of  its  seed  and  death.  In  many 
of  these  there  is  strong  root  and  leaf  development  the  first  year 
with  very  little  stem,  while  the  second  year  the  stem  develop- 
ment is  more  prominent,  the  flowers  and  seed  are  formed,  and 
the  plant  dies.  Examples  are  the  carrot,  turnip,  beet,  cabbage. 
The  evening  primrose  is  sometimes  a  biennial.  Winter  wheat  is 
usually  a  biennial.  When  sown  in  the  autumn  or  late  summer 
it  forms  strong  "  stools"  by  producing  numerous  branches  near 
the  ground.  When  sown  in  the  spring  it  becomes  an  annual, 
grows  more  quickly  into  the  long  stems,  and  stools  but  little. 
For  this  reason  spring  wheat  is  generally  used  for  spring  sowing. 
Those  plants  which  are  sometimes  annual,  sometimes  biennial, 
are  often  called  transition  forms.  Perennials  are  plants  which 
normally  live  several  or  many  years.  Examples  are  found  in 
most  of  the  grasses,  the  golden-rod,  wild  aster,  and  all  shrubs 
and  trees.  Some  plants  have  a  perennial  root  stalk  and  an 
annual  aerial  shoot,  as  in  the  mandrake,  jack-in-the-pulpit, 
wake-robin,  etc. 

37 


38  GROWTH  AND   WORK  OF  PLANTS 

61.  Principal    functions    of    the    stem. — The    stem    has 
several  kinds  of  work  to  do.     The  two  principal    functions   of 
ordinary  stems  are,  first,  support  for  the  leaves  so  that  they  can 
be  well  exposed  to  the  light  and  air,  and  second,  conduction  of 
water  and  food  substances  from  the  roots  tn  the  leaves,  and  of 
food  substances  from  the  leaves  to  the  roots  and  different  parts 
ofjlje-stem.     Other  functions  of  stems  will  be  seen  in  stuHymg 
the  specialized  kinds  of  stems. 

62.  Stems  respond  to  the  influence  of   light. — They  are 
sensitive  to  light  and  under  its  stimulus  they  turn  toward  the 
light.     This  is  well  seen  in  growing  plants  like  beans,  peas,  sun- 
flower, etc.,  especially  in  young  plants  when  all  the  leaves  are 
removed  and  the  plant  is  placed  near  a  well-lighted  window,  or 
in  a  dark  box  with  a  small  window  at  one  side. 

63.  Peculiarities  of  stems  grown  in  continued  darkness. 
— Stems  grown  in  the  dark  are  very  different  from  those  grown  in 
the  light.     They  lack  chlorophyll,  the  green  coloring  matter  in 
leaves  and  many  young  stems.     The  leaves  on  many  such  stems 
are  very  small,  and  the  stems  of  many  plants  are  long,  more 
slender,  more  watery  and  contain  less  plant  substance  than  the 
same  plants  grown  in  the  light.     In  the  light,  building  material 
is  formed  in  the  green  parts,  especially  in  the  leaves.     This  fur- 
nishes the  substance  for  building  material  especially  of  the  cell 
wall,   the  firm  and  hard  parts  of  the  stem.     Thus  under  the 
influence  of  light  the  stems  are  stockier,  shorter  and  firmer. 

64.  Types  of  stems. — There  are  several  types  of  stems  as 
regards  the  form  or  habit  of  the  stem  system.     Some  of  these 
types  are  well  shown  by  different  trees.     Observations  can  be 
made  on  these  in  the  fields,  parks  and  woods.     The  conical  type 
is  very  characteristic   of   many   spruces,   the   larch,    and   some 
other  coniferous  trees.     The  main  stem  or  trunk  is  straight,  con- 
tinuous through  to  the  topmost  part  of  the  tree,  and  is  often 
called  the  leader,  or  the  trunk  is  said  to  be  excurrent.     The 
branches  are  all  lateral  to  this  and  much  smaller.     The  lower 
branches  are  the   longer,  and  successive  branches  upward  are 
successively  shorter,  so  that  the  outline  of  the  tree  as  a  whole  is 


TYPES  AND   KINDS  OF  STEMS  39 

that  of  a  tall  cone.  The  oval  type  is  represented  by  certain 
oaks  especially  when  they  grow  in  the  open  where  they  are  not 
crowded  and  the  branch  system  is  free  to  develop  freely.  The 
columnar  type  is  represented  by  the  Lombardy  poplar,  where  there 
is  a  central  shaft,  the  leader,  and  numerous  small  branches 
which  are  nearly  erect  and  nearly  parallel  with  the  main  axis. 
The  diffuse  or  deliquescent  type  is  well  expressed  in  the  elm. 
The  branching  is  somewhat  dichotomous  and  diffuse,  the  main 
trunk  being  soon  lost.  The  branching  is  only  an  apparent,  not 
a  true  dichotomy.  The  buds  on  the  young  shoots  are  alternate 
and  two-ranked,  that  is,  regularly  in  two  rows  on  opposite  sides 
of  the  stem.  The  young  shoots  tend  to  be  somewhat  zigzag, 
with  a  bud  on  the  outside  of  each  angle.  The  axillary  terminal 
bud  develops  in  one  direction,  while  the  second  bud  develops  a 
shoot  which  diverges  in  the  other  direction,  thus  forming  an 
apparent  dichotomy. 

65.  Kinds  of  stems. — The  great  variety  of  stems  may  be 
grouped  together  under  the  head  of  kinds  of  stems.     For  example, 
the  floral  stem  or  floral  shoot  is  that  part  of  the  stem  whose  work 
it  is  to  bear  the  flower  or  flowers.     The  foliage  shoot  is  the  portion 
of  the  stem  which  bears  the  leaves  or  foliage,  and  is  often  very 
extensive.     Specialized  stems,  or  specialized  shoots,  are  those  stems 
which  are  unusual  either  because  of  their  peculiar  form  or  because 
of  the  work  which  they  perform,  as  the  cactus,  the  potato  tuber, 
etc.     In  fact  all  stems  properly  speaking  are  specialized  for  certain 
kinds  of  work.     Bud  shoots,  or  buds,  for^i  another  kind  of  stem. 
Within  each  of  these  kinds  of  stems  there  is  a  considerable  variety. 
The  pupil  should  study  a  number  of  each  kind.     In  the  study  of 
the  floral  shoot  we  are  concerned  chiefly  with  the  flower,  and  this 
topic  will  be  taken  up  in  Chapter  XVI. 

FOLIAGE   SHOOT. 

66.  Erect   stems. — The    erect    stems    are    self -supporting. 
Trees,  the  vast  majority  of  shrubs,  and  many  herbs  belong  to  this 
kind.     The  main  axis  is  erect  for  a  greater  or  lesser  distance,  but 
the  branching  often  soon  displaces  the  main  trunk,  and  the  various 


40  GROWTH   AND    WORK   OF   PLANTS 

stems  of  an  individual  plant  may  extend  in  various  directions. 
The  general  position,  however,  of  the  plant  is  erect.  Where  a 
number  of  individuals  start  very  close  together,  in  age  the  outer 
ones  may  lean  more  or  less  under  the  influence  of  light  and  the  need 
for  room.  This  is  true  with  many  shrubs  which  branch  near  the 
ground  or  send  up  many  stems  from  the  underground  portion. 
Erect  stems  are  self-supporting,  the  woody  and  supporting  tissues 
being  sufficiently  developed  to  give  great  strength  and  rigidity, 
while  the  proportion  in  size  and  height  is  in  harmony  with  the 
supporting  tissues. 

67.  Climbing  stems.  —  Climbing  stems  are  not  self-supporting; 
they  climb  upon  or  around  other  objects.  The  pumpkin,  the 
morning  glory,  the  grape,  Japanese  and  English  ivy,  climbing 
bitter  sweet,  climbing  poison  ivy,  the  rattan,  etc.,  are  examples. 
The  rattan  grows  in  India,  often  attaining  several  hundred  feet  in 
length.  The  more  slender  species  are  used  for  wickerwork,  etc. 
Climbing  stems  secure  themselves  to  the  object  of  support  in 
various  ways.  Root  climbers  develop  numerous  aerial  roots  from 
the  stem  which  take  hold  in  the  crevices  of  the  coarse  bark  of  trees, 
as  in  the  climbing  poison  ivy,  or  they  can  lay  hold  of  smoother 
surfaces  of  trees  or  walls,  as  the  English  ivy.  Tendril  climbers 
take  hold  of  the  object  of  support  by  long 
slender  outgrowths.  In  many  cases  these 
tendrils  are  modified  leaves  or  portions  of 
leaves.  In  the  pea  the  terminal  portion  of 
the  leaf  and  leaflets  (the  midribs)  forms 
the  tendrils  which  coil  around  the  object  of 
^support.  In  the  squash  and  some  other 
cucurbits  it  appears  that  the  tendrils  are 
the  main  veins  of  reduced  leaves.  In  the 
clematis,  or  virgin's  bower,  the  petiole  of  the 
leaf  acts  as  the  tendril  and  coils  around 
-fasts.  the  object.  The  dwarf  tropaeolum  climbs 

in  a  similar  way.  In  the  Japanese  (or  Boston)  ivy  the  ends  of  the 
branched  tendril  are  broadened  into  thin,  flat,  disk-like  objects, 
which  are  applied  closely  to  the  smooth  surface  of  the  wall  and 


u  j- 

Japanese  ivy  with  disk-like 

hold-f 


TYPES   AND   KINDS   OF   STEMS  4! 

hold  tightly  to  it.  The  tendrils  of  the  American  jvy  (Ampelopsis 
quinquefolia)  behave  in  a  similar  way.  Twining,  or  coiling 
climbers,  coil  around  the  object  of  support,  as  the  hop,  morning 
glory,  climbing  bean.  All  twining  stems  do  not  coil  around  the 
object  of  support  in  the  same  direction,  but  a  given  species  always 
coils  in  the  same  direction.  The  morning  glory  coils  from  right 
to  left,  i.e.,  against  the  sun,  while  the  hop  coils  in  the  opposite 
direction,  i.e.,  with  the  sun.  In  the  tropical  forests  climbing 
stems  reach  their  greatest  development.  Some  of  the  lianas  (as 
these  climbing  plants  are  called)  have  stems  the  diameter  of  large 
trees.  One  curious  one  (Copernicia  tectorum)  forms  a  network  of 
anastomosing  branches  around  palms. 


Fig.  42. 
Stolon,  or  runner,  of  strawberry. 

68.  Prostrate  stems. — Prostrate  stems  trail  or  "  creep  "  on  the 
ground.     The  dewberry  and  strawberry  are  examples  of  climb- 
ing land  plants.     These  are  also  called  stolons  from  the  habit  of 
creeping  on  the  ground  for  a  distance,  then  striking  root  and 
developing  a  cluster  of  leaves,  while  the  main  stem  continues  as 
a  creeper  and  strikes  root  again,  and  so  on.     The  water  fern 
(Marsilia)  is  a  good  example  of  a  prostrate  aquatic  plant. 

69.  Root  stocks,  burrowing  stems,  or  rhizomes. — These 
are  subterranean  stems.     They  may  be  long  and  extend  for  a 
considerable  distance  in  the  ground  as  in  the  mandrake,  false 
Solomon's  seal,  many  grasses,  the  bracken  fern  and  sensitive  fern; 
or  the  stem  may  be  short  and  thick  like  the  underground  stem  of 
the  wake  robin  (Trillium).     Such  underground  stems  are  called 
root-stocks.     Most  of  them,  as  in  the  case  of  the  mandrake,  false 
Solomon's  seal,  wake  robin  and  grasses,  have  erect  stems  which 
arise  as  branches  from  the  root-stock  and  bear  the  flowers  and 


GROWTH   AND    WORK  OF   PLANTS 


foliage  leaves,  while  scale  leaves  are  borne  on  the  subterranean 
stem.  Grasses  with  subterranean  stems  (root-stocks)  are  in  some 
descriptive  works  said  to  be  "  stoloniferous."  But  this  is  not  in 
accordance  with  the  strict  use  of  the  term  stolon  since  it  does  not 
apply  to  subterranean  stems.  The  root-stocks  of  the  bracken 
fern  and  sensitive  fern  do  not  bear  aerial  branches,  but  the  large 
leaves  which  arise  from  the  subterranean  stem  have  stout,  long, 
leaf  stalks  which  serve  to  lift  them  up  into  the  air  and  light. 

70.  Root-stock  of  Iris.— The  root-stocks  of  Iris  are  irregularly 
club-shaped,  with  prominent  concentric  rings  and  stout,  fleshy 

roots.  Branching  of  the  root- 
stock  takes  place  near  the  up- 
per end.  These  branches  arise 
in  the  axils  of  old  leaves  and 
first  appear  as  conical  buds. 
In  plants  a  few  years  old  the 
branching  system  is  readily 
seen.  In  the  depressions  the 
concentric  rings  are  the  scars 
formed  by  the  falling  away  of 
the  leaves,  the  scars  marking 
the  point  where  the  leaf  bases 
were  attached.  In  these  leaf 
scars  are  numerous  minute  pits, 
the  scars  of  the  nbro-vascular 
bundles  of  the  leaf. 

71.  Decumbent  stems. — These  are  stems  which  arise  in  an 
ascending  manner  and  then  curve  or  droop  to  the  ground,  where 
they  often  take  root  at  the  tip  and  form  here  a  new  decumbent 
stem,  so  that  the  plant  slowly  travels  and  spreads  over  the  ground. 
The   blackberries  and  raspberries  are   decumbent  stems.     The 
"  walking  "  fern  travels  in  a  similar  way  but  it  is  the  long  narrow 
leaf  which  is  decumbent.     The  tip  of  the  leaf  strikes  the  ground 
and  organizes  a  stem  which  develops  roots  and  new  leaves. 

72.  Crown  stems,  or  acaulescent  plants. — The  dandelion 
is  a  good  example  of  this  kind  of  stem.     These  are  sometimes 


Fig.  43- 
Root-stock  of  iris. 


TYPES  AND   KINDS  OF  STEMS 


43 


called  "  stemless  "  plants,  and  this  is  the  meaning  of  acaulescent 
plants.  The  plant  appears  to  be  composed  only  of  root  and 
leaves.  But  there  is  a  very  short  section  of  the  stem,  difficult  to 
define  its  limits,  between  the  root  and  leaves  and  to  which  they  are 
attached.  It  is  at  the  crown  of  the  root,  and  for  this  reason  such 
a  stem  may  be  called  a  crown  stem.  Many  biennials  have  crown 
stems.  The  beet,  turnip,  parsnip  and  carrot  are  also  examples, 
but  because  of  the  large,  fleshy  root  of  these  plants  they  are  some- 
times called  crown  tubers.  The  crown  stem  of  the  dandelion  is 
perennial  and  bears  the  foliage  leaves.  But  each  year  it  develops 
one  or  more  flower  stems  which  die  down  after  the  seed  ripens. 
In  the  fleshy  roots  mentioned  above,  during  the  second  year  a 
tall  leafy  stem  is  developed  which  bears  flowers  and  seed.  The 
fleshy  roots  are  reservoirs  for  the  storage  of  food  material  (see 
Chapter  II). 

SPECIALIZED    STEMS. 

73.  Bulbs. — A  bulb  is 
a  specialized  shoot  with  a 
very  short  stem  which  is 
covered  with  numerous 
overlapping  thick  leaves, 
as  in  the  onion,  hyacinth, 
lily,  tulip,  etc.  The  onion 
is  made  up  largely  of 
broad,  thick,  short,  fleshy 
leaves,  or  the  leaf  bases, 
which  overlap  very  closely 
and  make  a  more  or  less 
flattened  circular  or  oval 
body.  The  outer  leaves 
are  usually  dead,  thin, 
papery  and  brown.  A  longitudinal  section  through  the  middle 
shows  well  the  thickness  and  relation  of  the  leaves.  At  the  lower 
end  can  be  seen  the  flattened  very  short  stem  to  the  upper  surface 
of  which  the  leaves  are  attached,  while  the  roots  extend  from  the 


Fig.  44. 
Section  of  onion  "bulb,"  showing  thick  fleshy  leaves. 


44 


GROWTH  AND   WORK  OF  PLANTS 


Fig.  45- 
Easter  lily  "bulbs." 


lower  side  (fig.  44).  The  food  is  stored  in  the  fleshy  leaves.  It 
is  of  a  proteid  or  nitrogenous  nature,  i.e.,  it  contains  nitrogen  in 
addition  to  carbon,  hydrogen,  and  oxygen.  The  presence  of  pro- 

teids  can  be  shown  by  heating 

portions  of  an  onion  in  nitric 
acid.  The  liquid  becomes 
pale  yellow  in  color.  Adding 
a  small  quantity  of  ammonium 
hydrate  the  color  becomes 
orange.  The  lily  bulb  (caster 
lily,  fig.  45)  is  similar  to  that 
of  the  onion  but  the  thickened 
leaves  are  not  so  closely  and 
€ompactly  crowded. 

74.  The  corm. — This  is  a  short,  thick,  fleshy  shoot  in  which 
food  is  stored.     The  Indian  turnip,  or  Jack-in-the-pulpit,  is  a 
good  example.     This  is  circular  and  somewhat  flattened  or  oval. 
It  is  perennial,  increasing  gradually  in  size  usually  each  year  on 
the  upper  side,  while  the  lower  side  gradually  dies  off.     Prop- 
agation of   the  corm  usually  takes  place   by  the  formation  of 
small  corms  on  the  side.     These  eventually  separate  and  form 
new  plants.     New  corms  are  also  formed  by  the  germination  of 
the  seed. 

75.  Tubers. — A    tuber   is    a   fleshy   thickened   portion  of   a 
subterranean   stem   containing   large    quantities   of   plant   food. 
There  are  rudimentary  scale  leaves,  in  the  axils  of  which  are 
buds.     These  buds  often  resemble  an  eye,  as  in  the  potato  tuber, 
when  they  are   called  "  eyes."     The  potato   plant  has  slender 
underground  stems  as  well  as  aerial  stems.     It  is  on  the  ends  of 
these  underground  stems,  which  are  thicker  than  the  roots,  that 
the  potato  tuber  is  formed.     Some  of  the  starch  that  is  made  in 
the  leaves  during  the  day  is  transported  to  these  underground 
shoots  and  stored  up  in  the  tuber. 

76.  The  potato  is  an  interesting  plant   to  study. — The 
potato  plant  is  propagated  by  planting  the  tubers,  or  pieces  of 
them  containing  the  eyes.     Tubers  kept  in  a  warm  room  during 


TYPES  AND   KINDS  OF  STEMS 


45 


the  winter  often  "  sprout,"  the  sprouts  or  shoots  developing  from 
the  eyes.  Sometimes  when  kept  in  a  box  or  drawer,  even  in  the 
absence  of  light,  they  will  form  colorless  shoots  and  a  new  crop 
of  small  potatoes.  If  placed  in  a  vessel  in  contact  with  a  little 
water,  and  kept  in  a  warm  room  in  strong  light,  green  shoots  and 
leaves  will  develop,  and  many  interesting  experiments  can  be 
performed  with  them.* 

77.  The  sweet  potato  is  sometimes  called  a  "  root  tuber."  It 
is  not  a  true  tuber  since  it  is  an  enlargement  of  a  root  and  not  of 
a  stem.  Sweet  potatoes  are  propagated  by  planting  the  potato 


Fig.  46. 

Desert  vegetation,  Arizona,  showing  large  succulent  trunks  of  cactus  with  shrubs  and 
stunted  trees.     Open  formation.     (Photograph  by  Tuomey.) 

to  obtain  the  young  shoots,  large  numbers  of  which  spring  from 
the  fleshy  root,  not  from  true  buds,  but  adventitious  buds  are 
formed  in  the  tissue  of  the  root. 

78.   Cacti. — The  cacti  embrace  a  great  variety  in  the  form  of 
the  stem.     The  stems  are  greatly  specialized.     They  are  succu- 

*  See  "  Water  Culture  Method  for  Experimenting  with  Potatoes,"  Plant 
World,  n,  249-254,  1908. 


46 


GROWTH   AND    WORK   OF   PLANTS 


lent  (fleshy  and  contain  quantities  of  water)  stout  and  thick, 
with  a  thick  waxy  cuticle  on  the  surface.  The  stomates  are 
deeply  sunk  in  depressions.  These  characters  aid  the  plant  in 
the  conservation  of  water  which  is  of  great  importance  to  these 
plants  since  they  usually  grow  in  desert  or  dry  regions.  They 
are  further  specialized  in  that  they  do  not  hi  'e  green  leaves, 
the  function  of  the  green  leaves  being  performed  by  the  stem 
which  contains  the  chlorophyll.  In  some  species  the  prickles  or 
spines  which  are  so  numerous  on  the  cacti  are  supposed  to  rep- 
resent leaves  since  they  are  outgrowths  of  the  stem.  Some  of  the 
cacti  have  tall  stout  columnar  stems,  some  are  shaped  like  a 
melon  as  the  "  melon  cactus,"  others  have  branched  stems  with 

flattened  pear-shaped  joints  as  in 
the  prickly  pear  cactus.  This  is 
widely  distributed  in  dry  regions 
of  the  West  and  South.  Examples 
of  the  cacti  are  usually  to  be  found 
in  greenhouses.  Such  stems  are 
sometimes  called  condensed  stems. 

79.  Other  succulent  stems. — 
Some  succulent  stems  are  common 
in  regions  which  are  not  habitually 
dry.  The  purslane  is  a  common 
weed  in  the  northern  and  eastern 
United  States.  It  has  thick,  smooth, 
watery  stems,  and  thick,  small,  suc- 
culent leaves.  It  is  very  difficult 
to  kill  because  of  its  power  to  con- 
serve water.  The  houseleek,  live- 
forever,  stonecrops,  etc.,  are  other 
examples. 

80.  Leaf -like  stems  or  phylloclades. — In  these  the  leaves 
are  reduced  to  mere  bracts,  and  the  stem  or  branches  of  it  are 
broadened  and  flattened  so  that  they  resemble  leaves.  The 
gardener's  "  smilax  "  (Myrsiphyllum},  so  commonly  grown  in 
greenhouses,  is  a  good  example.  The  main  stem  is  slender  and 


Fig.  47- 
Phylloclades  of  smilax. 


TYPES  AND   KINDS   OF  STEMS  47 

cylindrical,  but  there  are  numerous  branches  which  are  leaf-like. 
They  are  known  to  be  branches  because  they  arise  in  the  axils  of 
small  scale-like  leaves.  The  asparagus  is  also  an  example  of  a 
plant  in  which  the  stem  has  taken  on  the  function  of  leaves, 
while  the  latter  are  rudimentary. 


OR   BUD   SHOOTS. 

81.  Buds  are  special  types  of  shoots  or  branches  containing 
the  delicate  growing  point  of  the  stem.     This  growing  point  is 
usually  protected  by  closely  overlapping  scales,  or  hairs,  or  in  some 
cases  it  lies  in  a  depression.     As  such  they  exist  in  a  resting 
condition  through  the  winter  in  some  climates,  or  through  dry 
periods  in  climates  where  this  is  the  resting  period  for  vegeta- 
tion.    Distinct  buds  are  also  usually  present  at  the  end  of  the 
growing  shoot  or  branch  throughout  the  growing  season.     The 
delicate  growing  point  organizes  the  young  leaves  which  arise 
near  its  apex,  and  the  stem  tissues  which  are  left  behind.     The 
growing  point  in  these  buds  is  protected  by  the  overlapping  young 
leaves,  sometimes  provided  with  numerous  hairs,  and  sometimes  in 
addition  by  a  waxy  or  resinous  or  gummy  substance.     As  to  their 
means  for  protection  buds  are  of  two  kinds,  covered  and  naked. 
The  covered  buds  have  a  coating  of  imbricated  or  overlapping 
scales,  while  buds  protected  by  cork  or  hairs  are  said  to  be  naked. 

82.  As  to  their  position  buds  are  axillary  when  they  arise 
as  usual  in  the  axil  of  a  leaf;   terminal  when  they  are  formed  at 
the  apex  of  a  shoot  or  branch;    accessory  when  there  are  more 
than  one  at  a  given  point,  one  above  the  other  in  the  axil  of  a 
leaf;    adventitious  when  they  arise  at  other  points  on  the  stem 
than  in  the   axils  of   the  leaves  or   apex  of  shoots,  i.e.,  at  any 
point  on  the  stem  or  root  or  leaf. 

83.  Protection  of  buds.  —  Since  in  our  climate  the  trees  and 
shrubs  form  the  buds  towards  the  end  of  the  growing  season,  the 
winter  is  the  resting  period  and  this  is  the  period  through  which 
the  delicate  growing  point  of  the  shoot  needs  protection  in  the  bud. 
The  covering  of  buds  by  the  closely  overlapping  scales,  and  by 
the  woolly  or  hair-like  covering  of  the  inner  scales  of  many  buds, 


GROWTH   AND    WORK  OF   PLANTS 


or  by  hairs  alone,  as  is  the  case  in  some  buds,  is  generally  supposed 
to  be  a  protection  against  freezing.  This  is  not  strictly  true,  for 
ice  is  abundantly  formed  within  the  buds  during  very  cold  weather 
even  in  buds  well  covered  with  scales  or  hairs.  It  is  rather  a  pro- 
tection against  the  effects  of  freezing,  or  more  properly  speaking, 
it  is  a  protection  against  the  loss  of  water  from  the  delicate  tissues 
of  the  bud.  This  protection  applies  then  to  buds  in  climates 
where  the  resting  season  for  vegetation  is  dry  and  hot  as  well  as 

in  climates  where 
the  resting  season  is 
very  cold.  When 
freezing  takes  place 
(in  plant  tissues  a 
little  below  the 
freezing  point  for 
water  outside)  the 
ice  is  rarely  formed 
inside  of  the  cells 
in  the  protoplasm. 
The  ice  forms  on 
the  outside  of  the 
cells  in  the  inter- 
cellular spaces.  As 
freezing  continues 
water  is  drawn  from  the  cells  and  added  to  the  ice  crystals  in  the 
intercellular  *  spaces.  The  effect  of  freezing  then  is  to  draw  water 
from  the  cells,  i.e.,  it  is  a  drying  effect.  If  the  buds  had  no  protec- 
tion on  the  outside,  the  ice  would  gradually  vaporize  and  escape. 
The  bud  coverings,  however,  prevent  excessive  loss  of  water,  and 
when  warmer  weather  comes  the  ice  crystals  in  the  intercellular 
spaces  melt  and  the  water  is  drawn  again  into  the  protoplasm  of 
the  cells  by  osmosis  (paragraph  352).  Bud  coverings  probably 
protect  the  young  growing  plant  from  mechanical  injury  also. 
For  the  study  of  buds  see  Chapter  VIII. 

*  See  "  Some  Studies  Regarding  the  Biology  of  Buds  and  Twigs  in 
Winter,"  Bot.  Gaz.,  41,  373-423,  1906. 


Fig.  48. 

Section  of  frozen  bud  of  Populus  dilitata  showing  ice  from 
water  drawn  from  the  bud  leaves  (from  K.  M.  Wiegand). 
The  white  crescents  are  masses  of  ice  between  the  bud  scales. 


TYPES   AND   KINDS   OF   STEMS  49 

GROWTH   OF   STEMS. 

84.  Definite  and  indefinite  growth. — In  woody  stems,  shrubs 
and  trees,  there  are  two  types  of  growth  in  length  of  the  new  shoots 
each  year,  definite  growth,  or  determinate  growth,  and  indefinite 
growth,  or  indeterminate  growth.  In  the  larger  number  of  trees 
and  shrubs  of  the  North  Temperate  region  the  growth  is  definite. 
It  is  usually  completed  by  the  middle  of  July.  A  terminal  bud 
is  formed  from  which  the  following  season  the  shoot  continues 
its  growth.  In  some  of  these  buds  all  the  leaves  of  this  shoot  for 
the  coming  season  are  already  formed  in  miniature  in  the  bud  and 
are  covered  and  protected  by  the  outer  dull  colored  scales.  Dur- 
ing the  growth  of  the  shoot  the  next  season  these  leaves  mature 
and  unfold  as  the  shoot  elongates,  and  then  a  new  terminal  bud  is 
formed.  In  other  cases  not  only  do  the  young  leaves  already 
formed  in  the  bud  expand,  but  new  leaves  are  formed  as  the  shoot 
elongates.  In  indefinite  growth,  however,  growth  in  length  of  the 
shoot  continues  until  late  in  the  summer  or  autumn,  and  the  ter- 
minal bud  as  well  as  the  terminal  portion  of  the  twig  dies.  One 
of  the  lateral  buds  then  acts  as  the  terminal  bud  to  continue  the 
growth  the  following  season.  In  the  spice  bush  a  considerable 
portion  of  the  dead  terminal  shoot  remains  and  the  following  year 
the  new  growth  comes  from  the  living  lateral  buds  some  distance 
back  from  the  tip.  In  the  elm  the  terminal  portion  of  the  shoot 
which  dies  is  small,  falls  away,  and  the  latest  lateral  bud  to  be 
formed  appears  to  occupy  the  end  of  the  shoot.  This  forms  an 
axillary  terminal  bud. 

•  85.  Annual  growth  of  stems. — Annual  growth  of  most  stems 
takes  place  in  two  directions,  in  length  and  in  thickness. 

86.  Growth  in  length. — In  the  case  of  stems  with  definite 
growth  there  are  external  marks  on  the  shoots  which  indicate  each 
year's  growth  for  several  years  until  the  bark  becomes  so  old  as 
to  obscure  the  marks.  These  marks  are  formed  by  the  scars  of 
the  bud  scales  when  they  fall  off  at  the  time  of  the  opening  of  the 
buds  in  the  spring.  These  are  known  as  scale  scars  or  ring  scars, 
because  they  form  closely  crowded  rings  on  the  shoot.  Stems 


50  GROWTH   AND   WORK  OF   PLANTS 

with  indefinite  growth  usually  do  not  show  these  annual  scale  scars, 
though  they  are  faintly  shown  in  some  stems  with  indefinite  growth 
which  have  axillary  terminal  buds,  as  in  the  elm.  In  pine  trees 
the  annual  growth  in  length  is  easily  shown  for  many  years  since 
one  whorl  of  branches  is  formed  each  year  from  a  whorl  of  buds 
just  below  the  terminal  bud.* 

87.  Growth   in   thickness. — Growth   in   thickness   of   most 
shrubs  and  stems  is  marked  by  "  annual  rings  "  seen  in  a  cross 
section  of  the  stem,  a  new  ring  of  tissue  being  added  each  year. 
These  rings  are  made  distinct  by  the  variation  in  the  compactness 
or  porosity  of  the  wood  formed  each  season,  those  vessels  (or 
"  pores  ")  in  the  wood  being  larger  which  are  formed  in  spring 
and  early  summer,  while  they  are  smaller  and  the  wood  more 
compact  which  is  formed  later  in  the  summer.     The  age  of  trees 
or  their  branches  can  be  determined  by  counting  the  number  of 
these  annual  rings. 

88.  Nodes  and  internodes  of  the  stem. — The  point  where 
each  leaf  is  borne  is  called  a  node.    The  space  between  two  succes- 
sive nodes  is  called  an  internode.     In  some  plants,  especially  the 
grasses,  corn,  wheat,  etc.,  the  nodes  are  very  distinct  since  they 
coincide  with  the  "  joint." 

*  These  buds  are  not  in  a  true  whorl  since  they  arise  in  the  axils  of  scale 
leaves  arranged  in  a  spiral  on  the  stem,  but  the  scale  leaves  are  very  numer- 
ous and  crowded  and  so  the  buds  appear  to  be  in  a  whorl. 


CHAPTER  VII. 


STRUCTURE  OF  STEMS  AND  THE  WATER  PATH  IN 

STEMS. 

89.  In  the  study  of  seeds  and  their  germination  (Chapters 
I  and  II)  it  was  found  that  certain  seedlings,  the  corn,  for  example, 
has  one  cotyledon,  while  the  pea,  bean,  etc., 

have  two  cotyledons,  or  seed  leaves.  Plants 
belonging  to  the  first  class  are  called  Mono- 
cotyledons, while  those  belonging  to  the  second 
class  are  called  Dicotyledons.  The  fact  that 
most  plants  of  the  first  class  have  one  coty- 
ledon, and  those  of  the  second  have  two 
cotyledons,  led  to  the  adoption  of  these  names. 
There  are,  however,  other  important  distinc- 
tions. The  anatomy  or  structure  of  the  plants 
belonging  to  these  two  classes  show  certain 
points  of  agreement.  Most  of  the  members 
of  the  monocotyledons  possess  one  type  of 
structure,  while  the  members  of  the  dicotyle- 
dons possess  another  type  of  structure. 

STRUCTURE    OF    THE    STEMS    OF 
MONOCOTYLEDONS. 

90.  The  corn  plant,  the  cereals  like  wheat, 
the  grasses,  etc.,  are  good  examples  of  mono- 
cotyledons; the  stem  is  distinctly  marked  off       com  plant,  a  mono- 
into  nodes,  or  joints,  and  internodes.      The 

leaf  is  attached  at  a  node.  The  three  parts  in  a  typical  leaf,  as  in 
the  corn,  are  as  follows:  The  sheath  surrounds  the  stem,  the  blade 
is  the  free  part  of  the  leaf,  the  ligule  is  a  slight  membranous 


52  GROWTH   AND    WORK   OF   PLANTS 

projection  at  the  junction  of  blade  and  sheath,  and  it  partly 
surrounds  the  stem. 

91.  Gross  structure  of  the  corn  stem  as  seen  in  cross 
section. — The  outer  hard  layer  is  called  the  rind.  The  soft 
pithy  portion  of  the  interior  forms  the  bulk  of  the  stem.  Scat- 
tered in  the  pith  are  minute  firmer  and  more  compact  points  as 


Fig.  50. 
Broken  corn  stalk,  showing  nbro-vascular  bundles. 

seen  in  cross  section.  In  old  corn  stalks  which  have  lain  in  the 
field  during  winter  and  a  part  of  the  following  season,  if  cut 
through  the  rind  with  a  knife  and  the  pith  within  broken,  these 
firm  portions  are  apt  to  pull  out  in  the  form  of  fibers  as  shown 
in  fig.  50.  "Stalks"  of  celery  (the  petioles  of  the  leaves)  are 
excellent  to  show  these  bundles  which  make  old  or  tough  celery 
"  stringy." 

92.  Fibro-vascular  bundles. — These  fibrous  portions  are 
made  up  of  several  kinds  of  elongated  cells  united  in  the  form  of 
a  bundle.  Some  of  the  cells  are  slender,  have  thick  walls,  and 
overlapping  ends.  They  are  woody  fibers  and  give  strength  to 
the  bundle.  There  are  other  elongated  cells  which  are  tubular 
and  are  joined  end  to  end  to  form  vessels.  There  are  other  kinds 
of  cells  too,  but  the  bundle  takes  its  name  from  these  two  sorts 
and  is  called  a  fibro-vascular  bundle.  The  water  which  passes 
from  the  roots  to  the  leaves  largely  passes  through  these  vessels, 


STRUCTURE  OF  STEMS 


53 


hence  the  term  vascular.  If  a  young  corn  stalk  or  other  leafy 
stem  is  cut  and  the  cut  end  placed  in  red  ink  or  in  a  solution  of 
a  red  analin  dye  like  eosin,  the  colored  liquid  rises  in  these  bundles 
and  colors  them,  while  the  pith  or  other  parts  remain  uncolored. 


rm 


Fig.  51. 

A ,  cross  section  of  the  stem  of  an  oak  tree  thirty-seven  years  old,  showing  the  annual 
rings,  rm,  the  medullary  rays;  m,  the  pith  (medulla).  B,  cross  section  of  the  stem  of  a  palm 
tree,  showing  the  scattered  bundles. 

93.  The  palm  stem. — Palm  trees  are  also  monocotyledons. 
In  fig.  51,  B,  is  shown  a  cross  section.     The  arrangement  and 
distribution  of  the  fibro-vascular  bundles  is  similar  to  those  in 
the  corn. 

94.  Microscopic  structure  of  the  corn  stem. — A  micro- 
scopic study  of  a  cross  section  of  a  corn  stem  shows  that  the 
pithy  portion  is  made  up  of  quite  large  cells  with  thin  walls,  the 
cells  being  equal  in  diameter.     This  kind  of  tissue   is  called 
parenchyma.     In  the  nbro-vascular  bundle  there  is  a  great  variety 
in  the  size  of  the  cells.     Near  the  center  of  the  bundle  is  a  group 
of  small  cells  with  thin  walls  filled  with  protoplasm  if  the  bundle 
is  not  too  old.     This  group  of  cells  is  the  cambium  portion  of  the 
bundle.     This  is  the  growing  part  of  the  bundle  so  long  as 
growth  takes  place.     It  is  the  region  where  the  cells  divide  and 
multiply  in  number,  i.e.,  growth  by  division  and  multiplication, 
and  should  be  distinguished  from  those  cells  which  have  ceased 
to  divide,  but  grow  by  enlargement.     Upon  one  side  of  the  bundle 
are  seen  the  large  vessels   with    the    smaller   fibers   and   some 
thin-walled  parenchyma  cells.     This  is  the  woody  portion  of  the 


54 


GROWTH   AND    WORK   OF   PLANTS 


bundle.     Upon  the  other  side  of  the  bundle  is  a  group  of  small 
cells  with  thick  whitish  walls,  the  bast  portion  of  the  bundle.     The 

dividing  cells  of  the  cambium  fur- 
nish the  cells  to  make  these  different 
elements  of  the  bundle  which  soon 
cease  to  grow  and  form  permanent 
tissue.  The  cambium  then  disap- 
pears; vessels,  bast,  and  thick-walled 
fibers  remain.  This  thick-walled 
fibrous  tissue  in  the  monocotyledons 
entirely  surrounds  or  encloses  the 
growing  tissue  and  other  elements 
of  the  bundle  and 
soon  prevents  far- 
Fig.  52.  ther  enlargement 

Transection  of  fibro-vascular  bundle  of  j 

Indian  corn,  a,  toward  periphery  of  and  expansion. 
stem;  g,  large  pitted  vessels;  s,  spiral  ves-  c  i  i  ji 

sel;  r,  annular  ve<*el;  /,  air  cavity  formed  ^UCh  a  bundle  in 
by  breaking  apart  of  the  cells;  i,  soft  bast,  i  •  i,  4-U  ,~U' 

a  form  of  sieve  tissue;  p,  thin-walled  paren-  which  the  Cambium 

is  enclosed  by  and 

passes  over  into  permanent  tissue  is  called  a 
closed  bundle.  Stems  with  closed  bundles  usually 
do  not  increase  in  thickness  after  the  formation 
of  the  permanent  tissue.  Monocotyledonous 
trees  like  the  palms,  therefore,  never  attain  the 
great  diameter  of  dicotyledonous  trees,  because 
the  trunks  cease  to  increase  in  diameter.  For 
this  reason  the  trunks  of  palms  are  of  nearly 
equal  diameter  while  dicotyledonous  trees  and 
conifers  which  have  open  bundles  (paragraph  98) 
have  tapering  trunks. 

95.  In  a  longitudinal  section  the  vessels  of 
the  bundle   are   seen  to   be   marked  in  various 
ways  by  thickenings  on  the  wall.     These  mark- 
ings  are  in  the  form  of  rings,  spirals,  pits,  trans-   p^016- 
verse  thickenings.     These  vessels  were  derived  from  cells  of  the 
fundamental  tissue  (parenchyma)  which  of  course  originally  came 


pig.  53. 


Olflpse^ionin0f 


STRUCTURE   OF  STEMS  55 

from  the  cambium  or  meristem.  At  first  they  elongate,  and  the 
cross  walls  at  their  adjacent  ends  dissolve  and  thus  make  long 
tubes  or  vessels  of  the  connecting  cells.  These  different  kinds  of 


Fig.  54- 
Uncoiled  spiral  ducts  of  Indian  lotus. 

vessels  can  often  be  found  in  the  same  bundle.  In  some  plants 
the  spiral  thickenings  on  the  vessels  are  so  regular  and  so  strong 
in  contrast  with  the  thinner  portions  of  the  wall  and  the  other 


Fig.  55- 
Photomicrograph  of  uncoiled  spiral  ducts  of  Indian  lotus. 

tissues  that  when  the  stem  is  broken  the  spiral  will  uncoil  in  long, 
delicate,  cobweb  threads.  This  is  shown  in  a  remarkable  way  in 
the  flower  stems  and  petioles  of  the  Indian  lotus  (figs.  53-55).  The 
rind  of  the  stem  is  cut  with  a  knife  and  the  stem  then  broken. 


56  GROWTH   AND    WORK   OF   PLANTS 

The  uncoiled  spiral  is  strong  enough  to  support  by  suspension  a 
piece  of  the  stem  2  cm.  to  4  cm.  long,  and  so  delicate  that  one 
cannot  see  the  means  of  support  at  a  little  distance  unless  held 
before  a  black  object  or  the  light.  Examined  under  the  micro- 
scope the  beautiful  spiral  markings  can  be  seen. 

STRUCTURE   OF  THE   STEM   OF  DICOTYLEDONS. 

96.  Gross  structure  of  the  stem  of  an  annual. — A  cross 
section  of  the  stem  of  a  dicotyledon  shows  a  very  different 
structure  (fig.  51,  A).  Leafy  shoots  of  dicotyledonous  stems  like 
the  garden  balsam  or  touch-me-not  (Impatiens),  bean,  sun- 
flower, etc.,  may  be  placed  with  the  cut  ends  in  red  ink  or  a 
solution  of  a  red  analin  dye.  After  several  hours  the  loss  of 
water  from  the  leaf  will  draw  the  colored  liquid  up  through  the 


Fig.  56. 

Xylem  portion  of  bundle.     Cambium  portion  of  bundle.     Bast  portion  of  bundle.    Section 
of  vascular  bundle  of  sunflower  stem. 

vascular  ducts.  This  will  stain  the  bundles,  and  also  the  veins 
of  the  leaves  in  many  cases,  so  that  the  color  is  easily  seen  through 
the  thin  overlapping  tissues.  If  shoots  with  white  flowers  are 
also  placed  in  the  dye  the  white  petals  will  become  stained.  If 
the  stems  are  now  cut  across  the  position  of  the  bundles  can 
be  seen.  Instead  of  being  scattered  without  order  through  the 


STRUCTURE   OF   STEMS  57 

stem  they  are  arranged  in  the  form  of  a  ring  about  midway 
between  the  center  of  the  stem  and  the  outside.  They  are 
arranged  in  a  concentric  ring  with  spaces  between  them.  The 
central  part  of  the  stem  is  the  pith  or  medulla.  The  portion 
outside  of  the  rings  of  bundles  is  the  cortex.  The  radiating 
strands  of  tissue  lying  between  the  bundles  and  connecting  the 
pith  with  the  cortex  are  the  medullary  rays. 

97.  Microscopic  structure  of  an  annual  stem. — The  pith 
cortex  and  medullary  rays  are  composed  of  thin  walled  cells  of 
nearly  equal  diameter  and  belong  to  the  fundamental  tissue  or 
parenchyma.     The  outer  layer  of  cells  is  the  epidermis.     In  some 
stems  just  underneath  the  epidermis  the  cells  for  several  layers 
have  walls  which  are  thickened  at  the  angles.     This  gives  addi- 
tional strength  to  the  stems.  - 

98.  The  fibre-vascular  bundle. — This  should  be  studied  in 
cross  and  longitudinal  sections.     In  cross  section  each  bundle  is 
seen  to  be  divided  into  two  parts,  an  outer  (toward  the  outside  of 
the  stem)  and  an  inner  one.     The  outer  portion  is  the  bast  portion, 
while  the  inner  is  the  woody  portion.     The  bast  portion  is  char- 
acterized by  numerous  bast  cells,  which  have  whitish  thick  walls, 
and  form  very  long  fibers.     In  the  wood  portion  are  the  vessels 
which  in  cross  section  appear  like  large  angular  or  circular  cells 
with  thick  walls.     Intermingled  with  the  vessels  are  the  thick 
walled  wood  fibers  and  some  thin  walled  parenchyma.     Between 
the  bast  and  woody  portions  of  the  bundle  there  is  a  group  of  cells 
with  very  thin  walls  and  rich  in  protoplasm.     These  cells  are 
usually  quite  regularly  arranged  in  rows  and  are  rectangular  in 
form.     This  is  the  cambium  portion  of  the  bundle.     The  cells 
of  the  cambium  grow  and  divide,  thus  increasing  in  number.     The 
older  ones  on  the  bast  side  of  .the  bundle  cease  to  grow  and  change 
into  bast  cells,  others  into  sieve  tubes,  etc.     The  older  ones  on 
the  wood  side  of  the  bundle  cease  to  grow  and  change  into  vessels, 
wood  fibers,  etc.     It  will  be  noticed  that  the  wood  and  bast  at 
no  point  meet  around  the  cambium  but  that  the  cambium  itself 
extends  across  the  medullary  ray  and  is  connected  with  the  cam- 
bium in  the  adjacent  bundles.     In  fact,  the  cambium  forms  a 


58 


GROWTH   AND    WORK   OF   PLANTS 


complete  ring  around  in  the  stem,  at  this  point  separating  the  bast 
and  wood  of  all  the  bundles.  The  bundle  is  not  therefore  closed 
but  is  open.  This  is  characteristic  of  the  bundles  of  the  dicoty- 
ledons as  distinguished  from  those  of  the  monocotyledons.  The 
stems  of  dicotyledons  can  therefore  increase  in  diameter  indefi- 


I 

tj 


Longitudinal  section  of  vascular  bundle  of  sunflower  stem;  spiral,  scalariform  and  pitted 
vessels  at  left;  next  are  wood  fibers  with  oblique  cross  walls;  in  middle  are  cambium  cells  with 
straight  cross  walls ;  next,  two  sieve  tubes,  then  phloem  or  blast  cells. 

nitely  as  long  as  growth  continues,  since  the  cambium  never  com- 
pletely passes  over  into  permanent  tissue,  and  extending  through 
the  bundle,  across  the  medullary  ray  into  the  adjacent  bundles, 
keeps  them  open.  A  longitudinal  section  of  a  bundle  will  show 
the  same  arrangement  of  the  cells,  and  will  give  an  idea  of  the 
length  of  the  different  elements,  and  show  the  markings  of  the 
vessels  and  the  character  of  the  sieve  tubes. 

99.  Structure  in  cross  section  of  perennial  woody  stems.— 
A  cross  section  of  a  stem  several  years  old  will  show  the  following 
structure.  In  trees  like  the  oak  the  chief  points  in  the  structure 
can  be  seen  readily  with  the  eye  or  with  the  aid  of  a  hand  or  pocket 
lens.  The  character  of  the  "  bark  "  will  depend  on  the  age  and 
the  kind  of  the  tree.  If  the  stem  is  only  a  few  years  old  the  bark 
will  be  green  and  soft.  This  soft  bark  is  made  up  of  the  bast 
portion  of  numerous  nbro-vascular  bundles  lying  side  by  side,  and 
in  it  are  the  sieve  tubes.  On  older  stems  the  outer  bark  is  dead 


STRUCTURE  OF  STEMS  59 

and  often  cracked  into  deep  furrows.  This  is  the  true  bark.  It 
is  formed  by  a  layer  of  cells  on  the  outside  of  the  bast  portion  called 
cork  producer.  The  soft  "  bark  "  lies  underneath  the  coarse  dead 
corky  bark  in  the  old  stems.  In  the  spring,  the  soft  bark  can  be 
very  easily  stripped  off  from  the  stems,  as  in  the  willow,  basswood, 
etc.  The  tissue  where  the  bark  parts  from  the  stem  when  stripped 
off  in  this  way  is  the  young  and  delicate  cambium,  which,  we 
found  in  paragraph  98,  forms  a  continuous  layer  entirely  around  the 
stem  between  the  bast  and  the  wood  of  the  bundle.  The  portion 
of  the  stem  lying  inside  of  this  layer  then  is  the  wood,  except  the 
central  portion  or  pith.*  The  wood  portion  of  old  trees  consists 
of  a  whitish  outer  portion  called  the  sap  wood,  while  the  darker 
inner  portion  is  the  heart  wood.  The  heart  wood  is  dead,  but 
in  the  sap  wood  there  are  many  living  cells  and  it  is  here  that  the 
rise  of  water  in  the  tree  takes  place.  No  rise  of  water  takes  place 
in  the  dead  heart  wood.  There  are  three  peculiarities  of  the  woody 
portion  of  such  a  stem  which  are  visible  to  the  eye.  First,  the 
slender  whitish  lines  which  radiate  from  or  near  the  pith  to  the 
outside.  These  are  the  medullary  rays  or  pith  rays  which  (para- 
graph 96)  lie  between  the  nbro-vascular  bundles.  They  consist 
of  parenchyma  cells  which  are  alive  in  the  sap  wood  and  usually 
dead  in  the  heart  wood.f  The  cells  of  the  pith  rays  are  very  much 
elongated  radially;  they  are  flattened  by  the  lateral  pressure  of  the 
bundles  and  they  present  the  smooth  shining  surfaces  in  radially 
split  wood:  second,  the  porosity  of  the  wood,  wrhich  appears  to  the 
eye  (unless  it  is  a  very  hard  compact  heavy  wood)  to  have  numer- 
ous minute  pores:  third,  the  presence  of  numerous  concentric 
rings,  called  annual  rings. 

100.  Growth  in  thickness  and  the  formation  of  annual 
rings. — In  woody  stems  the  nbro-vascular  bundles  lie  very  closely 
side  by  side  so  that  the  woody  part  of  one  bundle  practically 
touches  that  of  the  two  adjacent  ones.  They  do  not  quite  touch, 

*  The  pith  varies  greatly  in  extent  in  different  trees  and  shrubs.  In 
some  it  is  very  abundant,  as  in  the  elder,  sumac.  It  may  be  continuous, 
chambered  or  diaphragmed,  etc.,  in  different  species. 

t  In  some  trees  the  pith  ray  cells  remain  alive  for  many  years. 


6o 


GROWTH   AND    WORK  OF   PLANTS 


however,  for  the  pith  ray  is  between.  But 
the  parenchyma  of  the  pith  rays  is  squeezed 
into  thin  plates  by  the  crowding  of  the  bundles. 
This  brings  the  bundles  of  the  first  year's 
growth  of  the  stem  so  near  together  that  they 
form  a  ring  visible  to  the  eye.  Since  the 
bundle  is  an  open  one  the  cambium  grows 
each  year,  adding  on  new  wood  on  the  inside 
and  new  bast  on  the  outside.  This  causes 
the  growth  in  thickness  of  woody  stems  since 
each  successive  year  the  cambium  places  on 
a  new  layer  of  wood  on  the  outside  *  of  the 
old  and  a  new  layer  of  bark  on  the  inside  of 
the  old.  As  the  stem  increases  in  diameter 
new  bundles  arise  in  the  cambium  between 
the  old  ones  so  that  the  bundles  are  always 
crowded.  The  annual  rings  are  not  marked 
by  rings  of  different  bundles.  Each  bundle 
is  thin  and  becomes  very  broad  and  flat  radi- 
ally, by  the  constant  addition  of  new  wood  on 
the  outer  edge.  The  annual  ring  is  due  to 
different  rates  of  growth  of  the  wood  during  a 
single  season.  In  the  spring  and  early  sum- 
mer growth  is  more  rapid  and  the  vessels  are 
larger.  This  gives  great  porosity  to  the  new 
wood  formed  in  spring  and  early  summer. 
In  late  summer  growth  is  slower  and  the 
vessels  while  present  are  very  much  smaller 
so  that  the  late  summer  wood  is  quite  com- 
pact. The  annual  rings  are  then  made  up 
of  alternating  rings  of  porous  and  compact 
wood,  and  rings  of  each,  constituting  an 
annual  ring,  since  both  are  produced  in  one 
season. 
*  For  this  reason  dicotyledons  are  called  by  some  exogenous  (growing 

on  the  outside) ,  while  the  monocotyledons  are  endogenous  (growing  on  the 

inside). 


Fig.  58. 

Section  of  oak  tree  show- 
ing annual  rings  and  med- 
ullary rays. 


CHAPTER   VIII. 
WINTER   CONDITION   OF   SHOOTS   AND   BUDS. 

101 .  A  study  of  the  winter  habit  of  perennial  plants  shows 
some  very  interesting  adaptations  of  plants  to  meet  the  severe 
conditions  to  which  they  are  subjected  during  the  season.     The 
spring  and  summer  is  the  growing  season.     The  new  growth  is 
at  first  comparatively  tender,  with  an  abundance  of  water  and  a 
comparatively  small  amount  of  cell  wall  or  building  material  in 
the  shoots  and  leaves.     In  this  condition  vegetation  is  very  sus- 
ceptible to  either  extreme  cold  or  extreme   drought.     This  is 
occasionally  seen  in  our  climate  (temperate  zone)  when  there  is  an 
early,  warm  spring.     The  new  shoots  and  leaves  are  developed 
rapidly.     They  are  full  of  water  and  the  tissues  are  soft  and 
weak.     When  a  severe  frost  follows  it  often  works  great  injury 
to  the  new  vegetation,  the  new  leaves  and  shoots  of  hardy  trees 
and  shrubs  being  killed  and  drying  up,  presenting  a  very  un- 
sightly appearance.     The  same  effect  is  sometimes  produced  in 
some  plants  when  a  strong,  dry  wind  continuing  for  several  days 
often  withers  up  the  leaves  and  shoots  because  of  the  excessive 
loss  of  water  under  these  conditions. 

102.  If  vegetation   passes   this   critical   period  without 
injury  the  natural  processes  of  maturity  and  ripening  of  the  parts 
prepare  the  plants  for  the  long,  severe  winter  season.     Different 
plants   prepare    to    meet   this   season   in   different   ways.     The 
annuals,  which  form  little  wood  or  protecting  bark,  expend  their 
energy  in  the  production  and  ripening  of  seed,  and  then  the  plant 
dies.     The  seed,  or  fruit,  possesses  dry,  hard  walls,  and  the  liv- 
ing substance  in  the  embryo  passes  into  a  condition  in  which 
there  is  little  danger  from  either  dryness  or  extreme  cold.     In 
the  case  of  the  perennial  herbs,  the  annual  shoot  produces  its 
seed,  and  then  dies  to  the  ground,  while  the  underground  shoot 

61 


62  GROWTH   AND    WORK   OF   PLANTS 

or  root  is  protected  from  either  drought  or  cold.  The  evergreens 
like  the  pines,  spruces,  cedars,  the  laurels,  rhododendrons,  etc., 
have  thick  leaves  which  are  protected  by  thick  walled  epidermal 
cells,  which  in  turn  are  also  protected  by  the  cuticle,  a  coating 
of  a  waxy  substance  which  largely  checks  the  loss  of  water. 
The  protoplasm  also  undergoes  certain  changes  with  the  on- 
coming of  winter,  so  that  it  is  more  resistant  to  the  injuries 
accompanying  extremely  cold  weather. 

103.  The  deciduous  trees  and  shrubs,  those  which  shed 
their  leaves  in  the  autumn  and  winter,  show  a  very  interesting 
adaptation  to  meet  the  rigors  of  a  winter  season.     The  leaves 
are  usually  broad  and  thin,   and  are  especially  suited  for  the 
purpose  of  transpiration,  that  is,  the  loss  of  water.     By  the  death 
and  shedding  of  the  leaves,  deciduous  trees  and  shrubs  get  rid 
of  organs,  which,  if  they  remained  alive  and  active  during  the 
winter,  would  drain  so  much  water  from  them  that  they  would 
dry  out  and  die,  since  the  roots  during  the  cold  season  absorb 
but  little  water  from  the  soil  and  could  not  replace  that  lost 
through  the   leaves.     The   shoots   are   protected  by  the  matur- 
ing or  ripening  of  the  wood,  the  cell  walls  becoming  thick  and 
firm.     The   outer  portion  of   the   bark   has   thick  walled   cells 
which  are  dead  and  lose  most  of  their  water.     With  each  year 
this  bark  becomes  thicker.     This,  with  the  waxy  cuticle  on  the 
surface,  serves  to  protect  the  winter  shoots.     The  young  growing 
points,  however,  consist  of  delicate  masses  of  cells  rich  in  pro- 
toplasm and  with   an  abundance  of  water.     If  these  growing 
points,  or  buds,  at  the  ends  of  the  shoots  and  in  the  axils  of  the 
leaves  were  unprotected,  they  would  lose  a  sufficient  amount  of 
water  during  the  dry  and  freezing  weather  to  kill  them.     But 
they  are  protected  by  coverings  in  the  form  of  bud  scales,  hairs, 
or  by  both,  and  often  by  the  abundant  formation  of  a  waxy  or 
resinous  substance  between  the  scales  and  on  the  outside.     The 
bud  scales  also  afford  protection  to  the  delicate  growing  point 
from  mechanical  injuries. 

104.  The    effect    of    freezing    on    plant    tissue.  —  Very 
few  plants   are   killed   by   actual   cold   or   freezing  of  the  tis-   i 


WINTER   CONDITION   OF   SHOOTS  AND   BUDS       63 

sues.*  It  was  once  thought  that  in  the  freezing  of  plant  tissue  ice 
was  formed  inside  of  the  cells,  and  that  the  protoplasm  was  killed 
by  the  cold.  But  this  rarely  occurs.  The  water  freezes  on  the 
outside  of  the  cell  wall,  and  additional  water  flows  out  from  the 
inside  of  the  cell  and  continues  to  freeze  there  building  up  ice 
crystals  in  the  intercellular  spaces  (fig.  48).  If  the  freezing  con- 
tinues long  enough,  so  much  water  may  be  drawn  from  the  proto- 
plasm in  the  cell  as  to  make  it  too  dry  and  thus  kill  it.  When  the 
buds  freeze  the  ice  crystals  are  formed  in  the  intercellular  spaces. 
When  the  ice  crystals  thaw  the  water  is  slowly  absorbed  by  the 
protoplasm  in  the  cells  again  and  is  unharmed.  Were  it  not  for 
the  bud  scales  and  other  means  for  bud  protection,  the  water 
from  the  thawing  ice  crystals  would  evaporate  and  the  proto- 
plasm would  be  killed.  The  effect  of  freezing  on  plant  tissue  is, 
therefore,  in  most  cases  the  same  as  that  of  excessive  dryness. 

105.  Characters  of  winter  buds  and  shoots. — Winter  buds 
and  shoots  possess  certain  marks  and  other  features  which  are 
characteristic  of  the  different  kinds,  so  that  a  careful  student  of 
these  characters  is  enabled  to  tell  the  different  kinds  of  trees 
and  shrubs  from  the  winter  condition  of  the  shoots  and  buds.f 
Some  of  these  characters  are  as  follows:    The  surface,  whether 
smooth  or  rough,  shiny  or  dull,  the  color,  the  form  of  the  lenti- 
cels.     The   lenticels  are   minute  elevations  composed  of  corky 
tissue  with  a  minute  opening,  which  serves  the  purpose  of  an 
interchange  of  air  and  other  gases,  between  the  tissues  of  the 
shoots  and  the  outside.     The  shape  of  the  shoots  is  another 
character,  also  the  form  and  arrangement  of  the  leaf  scars,  with 
their  markings,  the  form  and  other  characters  of  the  buds,  etc. 
The  characters  of  the  following  shoots  will  serve  as  illustrations. 

106.  Shoots  of  the  horse  chestnut. — Terminal  buds.     The 
terminal  bud  where  well  formed  is  larger  than  the  lateral  buds. 
This,  as  in  other  similar  cases,  is  evidence  that  this  bud  will  con- 

*  See  "Some  Studies  Regarding  the  Biology  of  Buds  and  Twigs  in 
Winter,"  Bot.  Gaz.,  41,  373-423,  1906. 

t  See  "A  Key  to  the  Genera  of  Woody  Plants  in  Winter,"  3rd  edition, 
'.908,  by  Wiegand  and  Foxworthy.  Andrus  &  Church,  Ithaca,  N.  Y. 


64  GROWTH   AND    WORK  OF   PLANTS 

tinue  the  growth,  the  coming  year,  of  the  main  shoot,  and  that  the 
lateral  shoots  will  be  subordinate  in  size.  The  buds  are  well 
protected  by  brown,  overlapping,  external  scales  and  a  sticky, 
varnish-like  substance,  which  covers  them.  If  the 
scales  are  removed  one  by  one  their  position  and  rela- 
tion can  be  seen.  They  occur  in  pairs,  the  two  of  a 
pair  being  opposite,  and  each  pair  alternates  with  the 
pair  above  and  below.  Some  of  the  buds  are  leaf 
buds  while  others  are  flower  buds.  As  the  buds  open 
in  the  spring  it  can  be  seen  that  the  leaves  have  a 
similar  relation  to  each  other,  and  to  the  scales,  except 
that  they  are  farther  apart.  As  the  scales  fall  away 
they  leave  transverse  lines  on  the  shoot,  which  are 
crowded  and  in  the  form  of  ringmarks.  These  are 
the  scale  scars.  They  mark  the  end  of  one  year's 
growth  of  the  shoot  and  the  beginning  of  the  next. 
By  observing  these  ring  scars  on  the  shoot  the  age  of 
the  shoot  can  be  determined  for  several  years  back. 
If  the  shoot  is  cut  obliquely  at  different  ages  it  will  be 
seen  that  the  annual  rings  indicate  the  same  age  of 
the  shoot  as  the  scale  scars  do.  Lateral  buds.  The 
lateral  buds  are  opposite  and  arise  above  the  leaf 
scars.  The  larger  buds  are  on  the  last  year's  growth, 
and  those  nearer  the  terminal  bud  are  the  larger  and 
will  develop  into  lateral  branches.  Those  buds  which 
do  not  ordinarily  develop  into  shoots  are  latent  buds, 
and  if  the  terminal  and  larger  lateral  buds  are  re- 
moved by  cutting  off  the  part  of  the  shoot  which  bears 
them,  can  develop  into  shoots.  The  leaf  scars.  The 
leaf  scars  are  large  and  shaped  something  like  the 
Fig  59  bottom  of  a  horse's  foot  with  a  horseshoe  and  nails. 
Shoot  of  horse  The  series  of  pits  (bundle  scars)  mark  the  position  of 

chestnut.  . 

the  vascular  bundles  which  extend  from  the  stem  into 
the  petiole  of  the  leaf.  Scattered  over  the  surface  of  the  shoot 
are  numerous  minute,  grayish  or  dull  white  elevations,  the 
lenticels. 


WINTER   CONDITION   OF   SHOOTS   AND    BUDS        65 


107.  Shoots  of  the  lilac.— The  shoots  of  the  lilac  have  the 
same  arrangement  of  the  lateral  buds  and  leaf  scars  as  those  of 
the  horse  chestnut.     They  are  opposite  and  in  pairs,  and  each 
pair  alternates  in  position  with  the  pair  above  and 

below.  The  leaf  scar  is  much  smaller  and  semi-lunar 
in  shape.  The  outer  bud  scales  are  brown,  while  the 
inner  ones  are  green,  and  some  of  the  intermediate 
ones  have  brown  tips  and  green  bases.  There  is  one 
interesting  point  of  difference,  however,  between  the 
shoots  of  the  lilac  and  those  of  the  horse  chestnut. 
The  shoot  appears  to  have  a  pair  of  terminal  buds 
which  stand  slightly  divergent.  There  is  a  leaf  scar 
at  the  base  of  each  one  which  shows  that  these  buds 
are  axillary;  i.e.,  they  arise  in  the  axils  of  the  leaves. 
They  are,  therefore,  axillary  terminal  buds.  This 
would  indicate  that  the  true  terminal  bud  was  sub- 
ordinate. This  is  true.  If  we  search  carefully  between 
the  pair  of  axillary  terminal  buds  there  is  found  a 
minute  dead  terminal  bud  on  the  scar,  left  where  it 
has  fallen  away.  This  indicates  that  the  shoots  of 
the  lilac  have  indefinite  or  indeterminate  growth. 
Those  of  the  horse  chestnut  have  determinate  growth. 
The  pair  of  axillary  terminal  buds  of  the  lilac  form, 
the  following  year,  a  pair  of  shoots  which  diverge,  or 
fork.  Some  of  these  buds,  however,  are  flower  buds, 
as  can  be  determined  by  dissecting  them. 

108.  Shoots  of  the  elm. — The  elm  represents  still 
another  type  of  shoot,  as  shown  by  the  position  of 
the  buds.     The  buds  are  alternate,  and  are  situated 
in  two  rows  on  opposite   sides  of  the   shoot.     The 

shoots  are  more  or  less  zigzag  in  outline,  the  buds  situated 
at  the  angles  thus  formed.  On  the  ascending  or  horizontal 
shoots  the  rows  of  buds  are  lateral,  so  that  as  they  develop 
into  shoots  the  branching  system  cf  a  limb  presents  a  flattened 
outline,  which  is  more  marked  when  the  leaves  are  present,  since 
shoots  and  leaves  lie  in  nearly  the  same  plane.  On  either  side  of 


Fig.  60. 
Shoot  of  lilac. 


66  GROWTH   AND    WORK   OF   PLANTS 

the  leaf  scar  is  a  minute  scar,  the  stipule  scar,  which  marks  the 
location  of  small  delicate  outgrowths  (the  stipules)  at  the  base  of 
the  leaf  stalk,  which  fall  away  soon  after  the  opening  of  the  leaves 
in  the  spring.  The  larger  bud  at  the  end  of  the  stem  is  situated 
in  the  axil  of  a  leaf  scar.  It  is,  therefore,  an  axillary  terminal  bud. 
Close  to  it  and  on  the  opposite  side  from  its  leaf  scar  is  a  small  scar, 
which  marks  the  point  where  the  true  terminal  bud  was  seated 
and  which  has  fallen  away.  The  shoot  of  the  elm  has  therefore 
indefinite  growth.  In  the  spring,  when  the  new  shoots  develop, 
the  axillary  terminal  bud  and  the  bud  next  below  but  on  the  oppo- 
site side  of  the  shoot,  develop  with  nearly  equal  vigor,  and  thus 
diverge,  producing  a  fork.  The  result  of  this  is  the  diffuse  or 
deliquescent  stem  of  the  elm  (see  types  of  stems,  paragraph  64). 

109.  Shoots  of  the  butternut. — The  terminal  young  shoots 
of  the  butternut  are  of  a  dull  brownish  green  color,  while  the  older 
shoots  are  a  darker  brown.     The  surface  is  dotted  with  minute 
gray  or  whitish  points,  the  lenticels.     The  terminal  shoot  can  be 
determined  by  the  prominent  apical  bud,  which  is  long,  conical 
and  slightly  curved.     On  vigorous  shoots  the  annual  growth  can 
be  determined  by  the  presence  of  a  band  of  small  rings  which 
mark  the  scale  scars  of  the  previous  year's  bud.     The  leaf  scars  on 
the  shoot  are  very  peculiar  in  form;  they  are  somewhat  triangular 
in  outline.     Upon  the  gray  face  of  the  scar  are  several  dark  marks, 
a  V-shaped  mark  below,  and  a  small  round  dot  at  each  upper 
angle,  giving  to  the  scar  the  grotesque  appearance  of  the  face  of 
some  animal.     These  marks  are  the  scars  of  the  nbro-vascular 
bundles  which  extended  into  the  leaf.     Directly  above  each  leaf 
scar  is  a  bud.     This  is  the  bud  which  was  formed  in  the  axil  of 
the  leaf.     Often  above  this  is  another  bud,  a  supernumerary,  or 
accessory,  bud.     The  position  of  the  scars  shows  that  the  leaf 
arrangement  is  alternate  and  spiral,  for  a  string  passed  around 
the  stem  and  passing  over  each  leaf  scar  would  extend  in  a  spiral. 
The  bud  scales  occupy  similar  positions  but  they  are  very  much 
crowded. 

110.  Shoots  of  the  peach. — The  shoots  of  the  peach  tree  have 
a  shiny,  smooth  surface,  which  is  usually  reddish  or  reddish  green 


WINTER   CONDITION    OF   SHOOTS   AND    BUDS       6? 


Oak 


in  color.     The  extent  of  the  year's  growth  varies  from  a  few  inches 

to  several  feet  in  length,  according  to  the  position  of  the  shoot  on 

the  tree  and  the  vigor  of  growth.     The  buds  in  the  axils  of  the 

leaf  are  one  to  three  on  vigorous 

shoots,  usually  three.     The  middle 

one  represents  the  main  shoot;  the 

lateral  ones  are  branches  from  its 

base.    Often  the  lateral  ones  develop 

shoots  also,  but  when  they  are  much 

stouter  than  the  middle  one  they  are 

usually  flower  buds.     If  not  killed 

by  extreme  winter  cold  (say,  — 26° C. 

— 15°  F.  or  lower),  they  will  blos- 
som in  the  spring.  If  they  have 
been  killed,  the  flower  is  black.  This 
can  be  seen  by  removing  the  over- 
lapping scales,  or  by  cutting  it  open 
through  the  middle.  In  pruning, 
from  one-third  to  one-half  of  the  end 
of  these  new  vigorous  shoots  is  cut 
away  in  order  to  favor  fruit  develop- 
ment, and  to  admit  sunlight  to  the 
forming  fruit. 

111.  Shoots  of  the  sumac.*— 
The  shoots  of  the  sumac  also  have 
indefinite  growth,  and  the  terminal 
portion  therefore  dies  back  some 
distance  during  the  winter.  This 
dead  portion  is  very  slender  and 
short  and  very  easily  falls  away.  It 
is,  however,  often  attached  during 
late  winter,  and  may  have  remnants 
of  leaves  clinging  to  it.  Jarring  the  shoot  usually  causes  the  dead 
terminal  portion  to  fall.  Sometimes  the  shoot  will  die  back 

*  The  characters  will  vary  with  the  species.     The  species  dealt  with 
here  is  the  stag  horn  sumac,  Rhus  lyphina  =  R.  hirta  of  some  books. 


Fig.  61. 
Shoots  of  butternut,  oak  and  peach. 


68 


GROWTH   AND   WORK   OF   PLANTS 


farther  than  this  slender  terminal  portion.  The  sumac  is  further 
interesting  because  of  the  hairy  condition  of  the  shoots;  the 
absence  of  bud  scales,  their  function  being  performed  by  a  dense 
woolly  covering;  by  the  resinous  or  gummy  ex- 
udation where  bruised  or  cut,  and  by  the  large 
size  of  the  medulla  or  pith.  The  leaf  scars  are 
peculiar  in  that  they  nearly  surround  the  buds, 
but  are  open  above  and  nearly  heart  shaped. 

113.  Shoots  of  the  willow.  —  The  shoots  of 
the  willow  possess  an  axillary  terminal  bud  and 
the  dead  terminal  portion  of  the  shoot  is  crowded 
to  one  side.  The  growth  of  the  willow  shoot 
therefore  is  indefinite.  The  leaf  scar  is  semi- 
lunar  in  form  and  there  are  three  bundle  scars, 
one  below  and  one  at  each  end.  There  is  but 
a  single  brown  scale  on  the  bud,  and  it  fits  over 
the  bud  like  a  cap  or  hood.  On  removing  it  the 
character  and  condition  of  the  bud  within  is  seen. 
It  is  green  and  the  young  leaves  are  hairy.  In 
the  spring  when  growth  begins  the  bark  is  easily 
removed  from  willow  shoots.  The  willow  is  a 
splendid  example  of  the  formation  of  adventi- 
tious shoots  and  roots.  They  are  developed  in 
great  numbers  when  a  shoot  is  placed  in  water 
or  in  moist  ground,  and  the  willow  is  therefore 
very  easily  propagated  from  cuttings. 

113.  Leaf  arrangement  or  phyllotaxy.— 
The  arrangement  of  leaves  on  the  shoot  follows 
in  general  certain  well-known  systems.  While 
there  are  certain  variations  and  departures  from 
the  normal,  on  the  individuals  of  a  given  species 


Fig>  62' 


base  of  termini  mr-  the  arrangement  is  the  same.     The  arrangement 

tion  and  dead  leaf.         ^    ^    studied    Qn     leafy    shOOtS,    Or    On     winter 

shoots,  since  the  leaf  scars  and  axillary  buds  mark  the  position 
of  the  leaves.  Leaves  are  either  opposite  or  alternate.  The 
pairs  of  opposite  leaves  usually  alternate  at  right  angles  with 


WINTER   CONDITION   OF  SHOOTS  AND    BUDS       69 

adjacent  pairs.  The  alternate  leaves  are  arranged  in  a  spiral 
on  the  stem;  i.e.,  a  line  drawn  around  the  stem  from  left 
to  right  and  passing  over  the  leaf  scars  would  form  a  spiral. 
The  arrangement,  whether  on  the  opposite  or  alternate  plan,  is 
probably  the  result  of  natural  causes  in  the  origin  of  the  leaves 
on  the  small  growing  point  of  the  stem,  where  they  are  much 
crowded.  The  origin  in  some  such  regular  order  whether  on 
the  opposite  or  alternate  plan,  permits  a  large  number  in  a  given 
space.  Either  of  these  arrangements,  however,  gives  the  leaves 
a  better  light  relation,  as  will  be  seen  in  the  study  of  leaves, 
than  if  the  leaves  were  arranged  promiscuously,  or  all  in  a  line 
one  above  another.  The  influence  of  light  therefore  may  have 
had  some  influence  through  inheritance  of  a  favorable  position 
for  the  leaves. 

114.  In  the  case  of  the  elm  shoots,  if  the  end  of  a  cord  is 
pinned  on  a  leaf  scar  near  the  base  of  the  last  year's  growth, 
and  wound  around  the  stem  from  left  to  right,  passing  over  the 
successive  leaf  scars,  it  will  pass  once  around  the  stem  for  every 
two  scars.  This  arrangement  is  represented  by  the  fraction  £,  the 
numerator  denoting  the  number  of  turns  around  the  stem,  and 
the  denominator  indicating  the  number  of  leaf  scars  traversed 
in  order  to  reach  another  leaf  scar  directly  above  the  one  at  the 
starting  point.  In  the  sedges  and  in  the  American  white  helle- 
bore (Veratrum  viride}  there  will  be  one  turn  for  every  three 
leaves,  and  this  is  represented  by  £.  In  the  butternut,  oak,  etc., 
there  will  be  two  turns  of  the  spiral  for  every  three  scars  or 
leaves,  and  this  is  represented  by  £.  Now  we  find  this  curious 
relation.  If  we  add  together  the  numerators  and  denominators  of 
the  first  two  fractions,  the  result  is  as  follows:  i  +  5  =  f .  Now 
if  we  add  together  the  last  two  fractions  in  a  similar  way  it  gives 
a  fraction  which  represents  another  plan  of  arrangement  possessed 
by  many  shoots,  thus  \  %  f  =  f .  In  like  manner  $  J  f  =  -fg, 
which  represents  another,  and  so  on  for  several  other  known 
systems. 


CHAPTER   IX. 
LEAVES,   THEIR   FORM    AND  MOVEMENT. 

1.   THE   GROSS   PARTS   OF   THE   LEAF. 

115.  Blade  and  petiole.  —  The  majority  of  leaves  consist  of 
two  rather  distinct  parts,  —  the  blade  and  the  petiole.  The  blade 
is  the  thin,  expanded  portion;  the  petiole  is  the  stalk  which 

attaches  the  leaf 
to  the  stem.  The 
petiole  is  some- 
times absent,  in 
which  case  the 
blade  is  attached 
Fig.  63.  directly  to  the 

Leaf  of  hydrangea,  showing  blade  and  petiole. 


is  the  essential  part  of  the  leaf  physiologically,  and  therefore  in 
all  plants  where  the  leaf  performs  its  normal  work  (see  Chapter 
XI)  the  blade  is  usually  present. 

116.  Stipules.  —  With   many    leaves    there    are    also   present 
small  or  medium  sized  appendages  which  are  attached  one  on 
each  side  at  the  base  of  the  petiole,  or  they  are  attached  to  the 
stem  at  the  junction  of  the  petiole.     These  are  the  stipules.     The 
stipules  are  either  permanent  and  remain  attached  to  the  petiole 
during  the  life  of  the  leaf,  as  in  the  apple,  pea,  etc.  (figs.  65,  68), 
or  they  fall   away  early,  as  in  the   elm.     In  the   former  case 
they  are  usually  green;  in  the  latter  they  are  often  pale.     The 
stipules  are  sometimes  quite  large,  and  the  two  together  enclose 
the  leaf  in  the  bud,  as  in  the  tulip  tree,  and  the  point  of  attach- 
ment of  the  two  extends  entirely  around  the  stem.     In  the  false 
acacia  the  stipules  are  in  the  form  of  stout  spines. 

117.  Parts  of  the  leaf  in  the  Indian  corn  and  grasses.  — 
In  the  grasses  the  part  of  the  leaf  attached  to  the  stem  folds 

70 


LEAVES,     THEIR    FORM    AND  MOVEMENT 


completely  or  partly  around  the  stem  for  some  distance,  and  is 
called  the  sheath,  while  the  blade  is  free.  In  the  Indian  corn 
and  some  other  Gramineae 
there  is  a  membranous 
growth  arising  from  the 
junction  of  the  sheath  and 
blade  which  lies  close  around 
the  stem.  This  is  the  ligule. 
118.  Venation  of  leaves. 
-The  blade  of  the  leaf  is 
prominently  marked  by  lines, 
in  the  form,  usually,  of  eleva- 
tions, especially  on  the  un- 
derside, while  the  lines  are 
also  seen  distinctly  on  the 
upper  side  of  the  leaf.  These 
are  called  veins  of  the  leaf. 
Some  of  these  veins  are  quite  Fig.  64. 

large    and.   prominent,    while      Leaf  of  corn,  showing  blade,  sheath,  and  ligule. 


c. 


D. 


A.        ,  Fig.  65. 

A.  Leaf  of  apple,  showing  persistent  stipules  at  base  of  petioles,  a  pinnate,  reticulate, 
veined  leaf,  edge  serrate.  B.  Leaf  of  beech,  pinnate,  reticulate  venation,  edge  serrate. 
C.  Leaf  of  laurel,  edge  plain.  D.  Leaf  of  holly,  edge  spiny. 

others  are  smaller  and  less  conspicuous.    Within  the  veins  are  the 
vascular  bundles,  which  are  continuous  through  the  petioles  with 


GROWTH  AND   WORK  OF  PLANTS 


the  vascular  system  of  the  stem.  Water  and  food  substances  are 
carried  from  the  stem  through  them  and  distributed  to  all  parts  of 
the  leaf,  and  the  food  assimilated  in  the  leaves  is  carried  back 
through  the  bast  portion  of  the  bundles  to  supply  the  growing 
parts  of  the  stem  and  roots.  The  "  veins  "  also  assist  in  giving 
firmness  and  support  to  the  thin  and  broadly  expanded  blade. 

119.  Kinds  of  venation  in  leaves. — In  general  there  are  two 
kinds  of  venation  presented  by  leaves,  which  in  general  are  cor- 
related with  certain  characters  of  relationship  noted  in  stems  and 
seedlings.  The  venation  is  either  parallel  or  netted  (reticulate), 
so  that  we  speak  of  parallel  veined  leaves  and  netted  veined  leaves. 
In  the  former  the  veins  are  long,  regular  and  nearly  parallel  and 
are  characteristic  of  most  monocotyledons,  as  in  the  corn,  the 
cereals,  other  grasses,  palms,  etc.  There  are  two  kinds:  First, 
those  in  which  the  veins  all  run  from  the  base 
to  the  apex  of  the  leaf;  second,  the  pinnately 
veined,  or  feather  veined,  those  in  which  there  is 
a  mid-vein  running  from  the  base  to  apex,  and 
the  lateral  veins  are  parallel  and  run  from  the 
mid-vein  to  the  margin,  as  in  the  pickerel  weed 
and  the  banana.  Parallel  venation,  however,  is 
not  characteristic  of  all  monocotyledons,  since 
the  leaves  of  the  Indian  turnip,  or  Jack-in-the- 
pulpit,  have  netted  veined  leaves.  In  netted 
veined  leaves,  the  veins  do  not  run  with  such 
regularity,  the  main  veins  diverge  more  or  less 
and  their  branches  finally  anastomose  into  a 
very  intricate  network.  There  are  also  two 
kinds  of  netted  veined  leaves,  the  palmate  and 
the  pinnate.  Palmate  leaves  are  those  in  which 
the  main  veins  spring  from  the  petiole  and 
then  diverge  something  like  the  digits  of  the 
hand  (palm)  toward  the  margin  of  the  leaf,  as  in 
the  maple.  In  pinnate  leaves  there  is  a  main 
vein  which  extends  from  the  petiole  directly  through  the  middle 
line  of  the  leaf,  and  the  main  branches  from  this  arise  at  nearly 


Fig.  66. 

Leaf  ot  rubber 
plant,  a  pinnately 
veined  leal,  edge 
plane. 


LEAVES,    THEIR  FORM   AND   MOVEMENT  73 

right  angles  and  run  nearly  parallel  toward  the  margin  of  the  leaf, 
like  the  "  veins  "  in  a  feather  or  pinna.  Examples  are  seen  in 
the  oaks,  apple,  quince,  beech,  rubber  plant,  etc.  Netted  veined 
leaves  are  characteristic  of  the  dicotyledons. 


2.   FORM   OF   LEAVES. 

120.  Leaves  vary  greatly  in  form,  not  only  as  to  the  general 
outline,  but  also  as  to  the  character  of  the  margin  and  the  division 
of  the  blade.     The  multitude  of  these 

variations  it  would  be  out  of  place  to 
enumerate  here,  since  a  knowledge  of 
them  is  chiefly  of  value  in  descriptive 
work  and  in  the  determination  of  species. 
Some  of  the  more  general  types  may, 
however,  be  mentioned.  Some  of  the 
more  aberrant  variations  are  mentioned 
under  modifications  of  leaves.  There  are 
two  general  kinds,  simple  leaves  and 
compound  leaves. 

121.  Simple  leaves. — Simple  leaves 
are  those  which  consist  of  a  single  blade. 

The  blade  may  be  oval  in  outline,  or  Fig  6? 

heart-shaped,     elliptical,     lanceolate,      Leaf  of  Tropaeoium,  a  peltate 

'  '  '    leaf  with  palmate  venation. 

arrow-shaped,  remform  (kidney-shaped), 

etc.,  and  the  edge  may  be  plain,  or  irregular  when  the  margin  may 
have  the  appearance  of  being  cut  into  minute  teeth  like  the  cutting 
edge  of  a  saw  (serrate  leaves),  as  in  the  apple,  or  with  more  promi- 
nent teeth  (dentate  leaves),  or  with  rounded  teeth  when  the  margin 
is  scalloped  (crenate  leaves),  etc.  When  the  divisions  extend 
deeper  the  leaf  is  cut,  when  nearly  or  quite  halfway  to  the  midrib 
the  leaf  is  lobed,  when  halfway  or  more  cleft,  when  nearly  to  the 
midrib  parted,  and  when  the  divisions  extend  quite  to  the  midrib 
the  leaf  is  divided.  The  margins  of  the  lobes  or  divisions  may  then 
be  plane  or  serrate,  etc.  These  divisions  take  place  between  the 
more  prominent  veins  so  that  the  leaf  may  be  pinnately  lobed, 


74  GROWTH   AND    WORK   OF  PLANTS 

parted,  divided,  etc.,  or  palmately  lobed,  etc.,  according  to  the  kind 
of  venation. 

±22.  Compound  leaves. — Compound  leaves  are  those  leaves 
in  which  the  divisions  of  the  blade  are  complete  and  regular  and 
the  divisions  are  set  off  distinctly  from  each  other  somewhat  like 
distinct  leaves,  or  leaflets. 

±23.  Significance  of  leaf  division. — The  leaves  are  impor- 
tant organs  for  certain  kinds  of  work  for  the  plant.  Within  certain 
limits  the  work  of  the  leaf  is  in  proportion  to  its  spread  of  surface. 
Beyond  certain  limits  of  spread,  however,  thin  leaves  are  in  danger 
of  injury,  since  they  would  be  whipped  about  more  by  the  wind. 
Divisions  of  large  leaves  permit  the  currents  of  air  to  pass  with 


A. 


Fig.  68. 


A.  Rose  leaf,  pinnately  compound,  odd  pinnate,  hairy  stipules.  B.  Leaf  of  pea,  pinnately 
compound,  terminal  leaflets  replaced  by  tendrils,  leaf-like  stipules.  C.  Clover  leaf,  palmately 
compound,  persistent  stipules. 


less  danger  of  injury.  The  work  which  leaves  perform  in  con- 
junction with  light  is  very  important  and  the  leaves  must  have  a 
good  light  relation.  Divided  leaves  permit  the  light  to  shine 
through  to  leaves  below  which  otherwise  would  be  too  greatly 
shaded  were  the  large  leaves  continuous. 


LEAVES,    THEIR   FORM   AND    MOVEMENT 


75 


3.   FALL  OF  THE  LEAF. 

124.  Leaves  are  not  permanent  outgrowths  of  the  stem  as 

most  branches  are.  Their  origin  is  superficial  as  compared  with 
the  origin  of  a  branch,  and  they  sooner  or  later  fall  away  from  the 
stem.  In  many  trees  and  shrubs  the  leaves  formed  during  the 
growing  season  fall  at  its  close.  These  trees  and  shrubs  are  said 
to  be  deciduous.  The  stems  remain  bare  during  the  resting  season 
which  in  our  climate  is  the  winter  season.  In  the  spring  new  leaves 
are  again  formed  on  the  new  shoots.  Other  trees  and  shrubs  hold 
each  season's  crop  of  leaves  for  several  (two  to  four  or  more)  years, 
and  usually  one  crop,  the  oldest,  falls  away  each  year.  These  trees 
and  shrubs  are  said  to  be  ever- 
green, because  they  are  holding 
several  crops  of  green  leaves 
during  summer  and  winter,  as 
in  the  pines,  spruces,  firs, 
balsams,  rhododendrons,  etc. 
When  the  time  has  come  for 
the  leaf  to  fall,  a  separation 
layer  of  cells  is  formed  at  the 
junction  of  the  petiole  with 
the  stem,  and  the  leaf  falls 
away  leaving  a  scar  (the  leaf  Flg>  69'  . 

snoot  of  white  pine  with     needle    leaves. 

scar)    on    the    stem    with    a 

smooth  surface  (Chapter  VIII).  The  scars,  therefore,  enable  us 
to  determine  the  position  and  arrangement  of  the  leaves  of  decid- 
uous shrubs  and  trees  during  the  winter. 


4.   ARRANGEMENT  OF  LEAVES. 

125.  The  arrangement  of  leaves  on  the  stem  seems  to  follow 
certain  definite  laws,  and,  barring  accidents,  is  always  the  same 
for  a  given  species. 

126.  Opposite  leaves. — Leaves    are    opposite    on   the    stem 
when  two  arise  at  the  same  level,  or  node,  but  on  opposite  sides. 
The  milkweed  (Asdepias)  is  a  good  example,  but  there  are  many 


76  GROWTH   AND    WORK   OF   PLANTS 

others,  as  the  horse  chestnut,  lilac,  etc.  In  these  examples  each 
pair  is  at  right  angles  to  the  pair  above  and  below,  so  that  looking 
down  the  axis  of  the  stem  there  are  seen  four  rows  of  leaves. 

127.  Whorled  or  verticillate  leaves. — Leaves  are  whorled 
where  three  or  more  arise  at  the  same  level,  or  node,  on  the  stem, 
and  they  are  usually  equidistant  around   the   circumference  of 
the  stem.     The  Joepye-weed  (Eupatorium)  is  an  example. 

128.  Alternate  leaves. — By  far  the  larger  number  of  plants 
have  alternate  leaves.     There  is  but  one  leaf  at  the  same  level 
or  node.     Not  only  do   the   majority  of  plants   have   alternate 
leaves,  but  there  is  a  great  variety  in  their  arrangement,  though 
they  all  are  arranged  spirally  around  the  stem.     The  simplest 
arrangement  of  alternate  leaves  is  seen  in  such  an  example  as  the 
elm,  iris,  corn,  etc.     There  are  two  rows  of  leaves,  one  each  on 
opposite  sides  of  the  stem.     If  a  pin  is  thrust  through  the  end  of 
a  string  and  then  stuck  at  the  point  of  attachment  of  a  leaf,  or 
in  a  leaf  scar,  and  the  string  is  wound  around  the  stem  in  a  spiral, 
passing  across  each  successive  leaf  scar  or  point  of  attachment, 
the  string  will  cross  two  leaf  scars  for  each  complete  revolution 
around  the  stem.     This  gives  us  the  law  or  plan  of  arrangement 
of  alternate  leaves  of  the  elm  type  which  is  expressed  in  the  form 
of  a  fraction,  the  numerator  being  the  number  of  revolutions  the 
string  makes  around  the  stem  until  it  reaches  a  leaf  directly 
above  the  leaf  at  the  starting  point,  while  the  denominator  is 
represented  by  the  number  of  leaf  scars,  or  points  of   attach- 
ment, over  wrhich  the  string  passes  in  making  the  same  number 
of  revolutions,  not  counting  the  leaf  scar  which  served  as  the 
starting  point.     In  the  case  of  the  elm,  therefore,  the  plan  of 
arrangement  is  expressed  by  the  fraction  \  which  represents  also 
the   angle   of  divergence  of  successive  leaves  from  each  other 
around  the  stem.     This  is  the  two  ranked  arrangement.     The 
next   higher   arrangement   is   the   three   ranked,    shown   in   the 
sedges,   the   Veratrum  or  American  white    hellebore   (Veratrum 
viride)  in  swamps  and  damp  woods.     The  leaves  are  in  three 
rows,  and  the  arrangement  is  expressed  by  the  fraction  J.     The 
five  ranked  arrangement  is  shown  in  the  apple,  poplar,  etc.     Here 


LEAVES,    THEIR   FORM   AND    MOVEMENT  ?? 

the  spiral  makes  two  revolutions  for  five  leaves,  and  the  fraction 
is*. 

129.  Practical  studies  on  the  arrangement  of  leaves. — 

This  study  can  be  carried  on  in  the  winter  by  the  leaf  scars, 
though  a  study  during  the  growing  season  is  preferable  if  it  is 
possible.  It  will  be  found  profitable,  if  possible,  to  prosecute 
this  study  in  the  fields  or  parks,  when  the  students  can  make 
their  observations  and  notes  on  opposite,  whorled  and  alternate 
leaves  with  a  determination  of  the  rank  of  the  arrangement. 

5.   RELATION   OF   LEAVES  TO   LIGHT: 

130.  Position  of  leaves  with  reference  to  light. — One  of 

the  most  important  relations  of  the  leaf  is  its  relation  to  light, 
because  of  the  work  in  the  manufacture  of  sugar  and  starch 
(photosynthesis,  Chapter  XII).  It  will  be  seen  that  the  various 
arrangements  of  leaves  shown  in  the  preceding  paragraph  are  of 
great  importance  in  giving  them  a  suitable  light  relation.  This 
position  on  the  stem  obviates  the  too  great  shading  of  adjacent 
leaves.  A  more  important  relation,  however,  is  the  position 
which  leaves  take  in  response  to  the  stimulus  of  light.  The 
position  which  leaves  occupy  on  the  stem  is  governed  largely  by 
laws  of  growth  in  the  formative  tissue  in  the  bud.  The  position 
which  the  leaf  blade  takes  as  it  expands  is  in  response  to  light 
stimulus.  This  position,  in  general,  is  such  as  to  bring  the  broad 
upper  surface  of  the  leaf  so  that  the  stronger  light  rays  will  fall 
perpendicularly  upon  it,  since  the  work  of  the  leaf  which  is 
carried  on  jointly  with  light  may  be  most  effective. 

131 .  Since  the  stronger  light  rays,  when  we  consider  any  con- 
siderable period  of  time,  come  from  the  zenith,  most  leaves  have 
in  general  a  horizontal  or  nearly  horizontal  position.     But  there 
are  many  conditions  which  bring  about  a  different  result.     On  the 
edge  of  a  dense  forest  or  clump  of  large  plants,  or  where  for  other 
reasons  there  is  strong  shade  on  one  side,  lower  plants,  unless 
they  are  shade  plants,  have  their  leaves  turned  more  or  less  so 
that  they  face  to  one  side  to  receive  the  incidence  of  the  strongest 
light  rays. 


GROWTH   AND    WORK  OF   PLANTS 


132.  Position  of  the  leaves  of  "compass"  plants. — There 
are  certain  plants  like  the  prickly  lettuce  (Lactuca  scariola)  and 
the  "compass"  plant  (Silphium  laciniatum)  whose  leaves  often 
stand  so  that  they  point  north  and  south,  no  matter  on  which 

side  of  the  stem  they 
are  attached.  The 
leaves  at  the  same  time 
are  turned  on  edge,  so 
that  the  surfaces  face 
east  and  west.  This 
position  is  taken  by 
the  leaves  in  response 
to  light  and  not  be- 
cause of  any  magnetic 
influence.  The  sun- 
light at  midday  is  too 
strong  for  the  leaves 
and  the  leaf  is  stimu- 
lated to  turn  its  edge 
to  the  incidence  of  the 
strongest  rays  so  that 
they  glide  by  with  no 
injury  to  the  leaf. 
The  light  during  the 
morning  and  after- 
noon hours  is  not  so 
strong  so  that  no  injury 

comes  from  the  exposure   of  the  surface  at  this  time  of  day. 

When  these  plants  grow  in  the  shade   the  leaves  do  not  point 

north  and  south  and  the  blade  is  horizontal. 

133.  Movement   of   leaves  in  response   to   light. — When 
leaves  are  young  and  their  position  has  not  become  fixed,  they 
often   show  marked  movements   in  response  to  light   stimulus. 
While  many  plants  manifest  this  peculiarity,  it  is  more  marked  in 
some  than  in  others.     Seedlings  of  many  plants  when  placed 
where  they  receive  a  one-sided  illumination,  as  near  a  window, 


Fig.  70. 

Prickly  lettuce  (Lactuca  scariola),  a  compass  plant, 
showing  side  and  edge  view. 


LEAVES,    THEIR   FORM   AND    MOVEMENT  79 

or  in  a  box  open  only  on  one  side,  the  leaves,  as  well  as  the  stems, 
turn  so  as  to  face  the  light.  If  the  position  of  the  seedlings  is 
changed,  the  leaves  will  turn  again.  In  the  sunflower  plant 
throughout  its  growth  the  younger  leaves  "  follow  the  sun"  all  day 
on  bright  days.  The  leaves  near  the  upper  end  of  the  stem  are 
drawn  somewhat  together,  so  that  they  form  a  rosette,  and  turn 
so  that  their  upper  surfaces  face  toward  the  rising  sun,  the  stem 
also  turning  to  assist  in  bringing  them  into  this  position.  This 
rosette  of  leaves  then  "  follows  the  sun"  all  day  and  at  sunset  it 
is  facing  the  west.  After  sunset  the  stem  straightens  up,  and  the 
leaves  assume  a  horizontal  position  because  the  strongest  rays  of 
light  are  now  from  the  zenith.  On  cloudy  days  the  leaves  remain 
in  this  horizontal  position.  Many  other  plants  show  this  same 
peculiarity,  the  cotton  plant,  ragweed,  sweet  clover,  and  especially 
those  plants  belonging  to  the  family  known  as  sensitive  plants, 
and  to  the  legumes  or  Leguminosae. 

134.  Night  and  day  movements  of  leaves. — While  leaves  are 
very  young,  as  in  the  bud,  or  plumule,  growth  of  the  cells  is  usually 
more  rapid  on  the  under  side  than  on  the  upper  side  of  the  leaf. 
This  causes  the  leaves  to  bend  upward  or  inward  toward  the  axis 
of  growth  of  the  stem.  During  later  growth,  however,  growth  is 
more  rapid  on  the  upper  side,  and  this  causes  the  leaves  to  "open" 
from  the  bud  and  to  extend  outward  or  even  to  bend  downward. 
This  upward  growth  tendency*  of  leaves  in  the  bud  is  an  advantage 
to  the  younger  leaves  and  to  the  growing  point  of  the  stem  since 
they  are  protected  from  drying  out  when  in  the  delicate  stage. 
When  the  downward  growth  comes  into  play  the  leaves  are  usually 
held  in  a  horizontal  position,  and  do  not  turn  downward  during 
the  day,  because  the  stimulus  of  light  (see  preceding  paragraph) 
holds  them  in  the  most  favorable  light  relation.  But  at  sunset  the 
young  leaves  of  many  plants,  and  all  leaves  of  certain  sensitive 
plants,  turn  downward,  because  the  stimulus  of  light  is  removed 

*  The  tendency  of  leaves  to  turn  upward  during  early  growth  is  called 
hyponasty,  or  hyponastic  growth.  The  tendency  later  to  turn  downward 
by  greater  elongation  of  the  cells  on  the  upper  surface  is  called  epinasty* 
or  epinastic  growth. 


80  GROWTH   AND    WORK   OF   PLANTS 

and  the  tendency  to  downward  growth,  which  was  overcome 
during  the  day,  now  produces  its  effect.  On  the  following  day, 
however,  the  light  stimulus  again  overcomes  this  downward 
growth  and  lifts  the  leaf  again.  This  drooping  of  leaves  at 
night  is  often  called  "  sleep  of  plants."  There  is  an  advantage 
to  the  plant  in  this  drooping  position  of  the  leaf  at  night,  since 
radiation  of  heat  is  less  than  if  the  surface  were  exposed  to 
the  zenith. 

135.  Movement  of  leaves  in  response  to  touch. — Some 
plants  are  very  sensitive  to  touch.  Remarkable  among  these  are 
the  "  sensitive  "  plants.  A  good  example  of  sensitive  plants  is 
the  Mimosa  pudica  so  often  grown  in  greenhouses.  The  leaves 
are  twice  compound  and  the  pinnules  (secondary  leaflets)  are 
in  pairs.  If  one  of  these  terminal  leaflets  be  pinched  with  the 
fingers  or  with  a  pair  of  forceps,  the  first  pair  of  leaflets  close, 
or  fold  together  above  the  mid-vein  of  the  pinna.  This  is  fol- 
lowed by  the  second  pair  and  so  on,  and  all  the  pairs  of  leaflets  on 
this  pinna  closing  in  succession.  When  the  last  pair,  the  one  at 
the  base,  has  closed,  all  the  pinnae  then  move,  closing  in  together, 
and  the  pairs  of  leaflets  on  the  other  pinnae  then  commence  to 
close  beginning  at  the  basal  pair  and  extending  to  the  terminal 
one.  Soon  also  the  entire  leaf  drops  down  from  its  point  of  at- 
tachment on  the  stem.  If  the  plant  is  jarred,  all  the  leaves  droop 
and  the  leaflets  close.  At  the  base  of  each  petiole  on  the  underside 
near  the  point  of  attachment  with  the  stem  there  is  an  enlargement, 
called  a  cushion  (pulvinus)  which  controls  the  movement  by  the 
contraction  or  collapse  of  its  cells.  There  are  similar  cushions  at 
the  base  of  the  leaflets  and  pinnae.  At  night,  or  when  placed  in 
darkness,  the  leaflets  close  up,  and  the  leaves  droop,  opening  up 
again  with  the  coming  of  light.  During  the  day  if  the  sunlight  is 
too  strong,  the  leaves  adjust  themselves  to  the  profile  position,  i.e., 
with  the  edge  towards  the  source  of  strongest  light.  When  the 
soil  becomes  too  dry  and  the  plant  is  in  danger  from  loss  of  water, 
some  or  all  of  the  leaflets  close  and  the  leaf  droops,  regulating  itself 
according  to  the  degree  of  dryness  or  drought,  since  in  the  closed 
position  the  leaves  lose  water  less  rapidly. 


LEAVES,    THEIR  FORM   AND    MOVEMENT 


Si 


136.  Relation  of  leaves  to  light.  —  This  is  preeminently  a 
subject  for  field  or  outdoor  study.      Observations  show  that  leaves 
assume  the  most  advantageous  arrangement  and  position  to  receive 
the  best  lighting.     In  many  cases,  when  the  leaf  arrangement  on 
the  stem  may  be  three,  five  or  eight  ranked,  the  leaf  blades  may  be 
all  arranged  in  a  single  plane,  to  receive  the  light  from  one  direction. 
This  often  occurs  in  woods  or  groves,  the  petioles  of  the  leaves 
twisting  so  as  to  allow  the  blade  the  most  favorable  position. 
Mosaics  or  patterns  are  formed  where  a  number  of  leaves  on  a 
single  shoot  lie  so  that  they  are  fitted  in  almost  like  pieces  of  mosaic 
and  so  that  there  is  very  little  shading  of  adjacent  leaves.     Fit- 
tonia  grown  in  greenhouses  is  a  splendid  example.     Rosettes  are 
formed  when  the  leaves  are  crowded  on  the  stem  near  the  ground 
in  the  form  of  a  rosette.     Imbricate  patterns  are  seen  where  the 
leaves  are  not  so  closely  crowded,  but  overlap  something  like 
shingles  on  a  roof  so  that  light  can  reach  the  leaves.     In  the  radiate 
pattern  the  leaves  radiate  in  all  directions  from  horizontal  to  the 
vertical  and  thus  obtain  a  good  light  relation,  as  in  the  screw  pine 
(Pandanus)  often  grown  as  an 

ornamental  plant. 

137.  Irritability   of   ten- 
drils and  twining  stems.  — 
When  a  tendril  or  a  twining 
stem,    as  it   slowly    swings 
around,   comes    in   touch    or 
contact  with  some  object,  this 
contact  stimulus  causes  it  to 
bend    at  this  point  bringing 
new  points  in  contact  so  that 

trap 

the  tendril  Or    Stem    then  Coils   Pul.a)-  showing    winged     glandular   hairs  folding 

petiole      and      toothed     inward  as  a  result  of  a 

lo 


Fig.  71. 

Leaf    of    Venus    fly- 
trap   (Dionaea 


Fig.  72 

Leaf   of   Drosera  ro- 
tundifolia,  some  of   the 


lobes- 


stimulus. 


around  the  object  of  support. 

138.  Response  of  insectivorous  plants  to  touch.  —  Remark- 
able movements  are  shown  by  the  leaves  of  some  insectivorous 
plants.  In  the  Venus's  flytrap  (fig.  71)  the  terminal  part  of  the 
leaf  is  shaped  like  a  steel  trap.  The  blade  is  broad  and  the  margin 
rounded  and  beset  with  numerous  hairs  or  spines  resembling  the 


82  GROWTH   AND    WORK   OF   PLANTS 

teeth  of  a  steel  trap.  Upon  the  upper  face  of  each  side  of  the  leaf 
are  three  prominent  hairs.  When  these  hairs  are  touched  the 
second  time,  the  leaf  suddenly  closes  like  a  trap.  Flies  which 
alight  on  the  leaf  are  thus  caught  and  pressed  between  the  folded 
leaf,  and  the  leaf  excretes,  through  special  glands,  juices  which 
digest  portions  of  the  insect,  which  are  then  absorbed  by  the  leaf 
and  used  for  food.  The  sundew  has  a  rounded  or  elliptical  leaf 
blade  covered  with  long  glandular  hairs  which  excrete  a  sticky 
substance.  When  an  insect  alights  on  the  leaf  the  sticky  substance 
holds  it,  and  the  hairs  and  leaf  slowly  fold  inward  around  the  insect 
and  it  is  digested  by  the  glandular  juices. 


CHAPTER  X. 
LEAVES,  THEIR    STRUCTURE  AND   MODIFICATIONS. 

139.  The  leaf  is  an  organ  of  a  plant  which  performs  several 
kinds  of  very  important  work.     Its  structure  is  remarkably  well 
adapted  for  these  kinds  of  work  and  also  for  its  own  protection, 
as  well  as  for  the  protection  of  the  plant  against  certain  un- 
favorable conditions  of  the  environment.     A  study  of  this  struc- 
ture is  necessary  to  a  clear  idea  of  the  work  of  the  leaf. 

1.    STRUCTURE    OF   LEAVES. 

140.  The  epidermis. — The  epidermis  is  the  outer  layer  of 
cells;  the  upper  and  lower  epidermis  covers  the  upper  and  lower 
surfaces  of  the  leaf  respectively.     The  epidermal  cells  are  usually 


Fig.  73- 
Portion  of  epidermis  of  ivy,  showing  irregular  epidermal  cells,  stoma  and  guard  cells. 

devoid  of  chlorophyll.  The  cells  are  usually  thin,  and  flat  in 
proportion  to  their  extent.  Viewed  on  the  surface,  as  they  can 
be  seen  by  stripping  off  a  portion  of  the  epidermis,  the  cells  in 
many  plants  are  seen  to  be  very  irregular  in  outline,  as  in  fig.  73. 

83 


84 


GROWTH   AND    WORK   OF   PLANTS 


Fig.  74- 

Cross  section  of  leaf  of  wintergreen. 
CM.,  cuticle;  Epid.,  epidermis;  v.d., vascular 
duct;  In/,  c.  sp.,  intercellular  space;  L.  ep., 
lower  epidermis;  St.,  stoma. 


When  viewed  from  the  edge,  as  seen  in  a  cross  section  of  the  leaf 
(fig.  74),  they  appear  quite  regular  and  rectangular. 

141.   The  cuticle. — Upon  the  outside  of  the  epidermal  layer 
of  cells  is  a  more  or  less  thickened  deposit  of  a  waxy  nature, 

the  cuticle.  This  is  extremely 
thin  in  some  plants  (shade  plants, 
especially  in  moist  regions),  while 
in  others  it  is  quite  thick,  as  in 
the  cabbage  (and  in  plants  of  dry 
regions).  When  the  cuticle  is 
highly  developed,  as  in  the  cab- 
bage plant  and  onion,  it  is  diffi- 
cult to  wet  the  leaf,  since  the 
water  rolls  off  so  easily  from  the 
smooth,  waxy  surface. 

142.  The  stomates. — When 
the  epidermis  is  viewed  from  the 
surface,  as  in  fig.  73,  here  and 
there  are  seen  peculiar  and  quite  regular  cells  in  pairs  surround- 
ing a  minute  opening  in  the  epidermis.  This  is  a  stomate,  and 
the  cells  which  surround  the  minute  opening  are  the  guard  cells. 
In  profile  view  each  guard  cell  is  nearly  semi-circular;  the  twro 
fitting  together  form  a  subcircular  or  subelliptical  figure.  When 
seen  in  a  cross  section  they  are  quite  different  in  form,  being 
somewhat  rectangular  with  an  irregular  outline  next  the  opening. 
Their  form,  structure,  and  relation  to  the  surrounding  cells  of  the 
epidermis  is  such  that  in  dry  periods  the  stomates  often  close  and 
check  the  loss  of  water  by  the  plant.  Under  such  conditions  the 
guard  cells  lose  part  of  their  turgidity,  and  their  form  so  changes 
that  their  inner  walls  touch  and  close  the  opening.  When  the 
plant  has  an  abundance  of  water  the  guard  cells  absorb  enough  to 
make  them  turgid,  and,  in  swelling,  their  form  and  the  thickness 
of  the  walls  causes  them  to  arch  away  from  each  other  and  open 
the  stomate. 

143.  Epidermal   outgrowths,  hairs,  glands,  etc. — Leaves 
are  either  smooth,  or  hairy,  or  rough  from  other  outgrowths  of 


LEAVES:   STRUCTURE  85 

the  epidermal  cells.  These  outgrowths  are  in  the  form  of  hairs 
(long  slender  cells  or  rows  of  cells),  glands  (special  cells  for  excret- 
ing various  substances)  and  scales  (as  in  Shepherdia}.  The  hairs 
are  simple  or  branched  (in  the  mullein),  some  of  the  latter  being 
star-shaped  (as  in  some  oaks).  These  hairs  and  scales  aid  the 
leaf  in  retaining  moisture  since  evaporation  of  moisture  from  the 
surface  is  hindered. 

144.  Structure  of  the  leaf  in  cross  section. — The  epider- 
mis and  guard  cells  as  seen  in  a  cross  section  of  a  leaf  have  been 
described  above.     The  interior  portion  of  the  leaf  consists  of  the 
mesophyll  and  the  fibro-vascular  bundles.      These  may  be  studied 
in  cross  and  longitudinal  section  according  to  the  way  the  veins 
run  in  the  portion  of  the  leaf  sectioned;  and  the  parts  in  general, 
the  wood  portion  with  its  vessels  and  wood  fibers,  and  the  bast 
portion  with  its  bast,  can  be  made  out  by  consulting  paragraphs 
94-98.     The  mesophyll  usually  consists  of  two  kinds  of  paren- 
chyma cells,  —  the  palisade  layer  of  cells  , .  .„, 
and  the  loose,  spongy  tissue.     The  pali- 
sade layer  of  cells  is  found  usually  just 

beneath  the  upper  epidermis.  It  consists 
of  elongated  cells  lying  closely  side  by 
side  and  perpendicular  to  the  epidermis. 
Sometimes  there  are  two  layers  of  pali- 

Section  of  ivy  leaf,  palisade  cells 
Sade  Cells;  in  the  COmpaSS  plants,  One  above,  loose  parenchyma,  with 

large  intercellular  spaces  in  center, 
layer  On  each  Side  01  the  leaf.  The  Epidermal  cells  on  either  edge. 

with  no  chlorophyll  bodies. 

remaining  part  of  the  mesophyll  is  the 

loose  parenchyma,  so-called  because  the  intercellular  spaces  are 
large,  thus  giving  the  cells  a  loose  arrangement.  These  inter- 
cellular spaces  connect  throughout  the  leaf  and  also  with  the 
stomates.  They  thus  provide  for  aeration  of  the  leaf,  for  the 
entrance  and  escape  of  gases  in  photosynthesis  and  respiration, 
and  for  the  escape  of  moisture. 

145.  The  chlorophyll  bodies. — The  green  color  of    leaves 
(as  well  as  of  other  parts  of  plants  except  in  some  rare  cases) 
resides  in  definite  bodies  called  chlorophyll  bodies.     These  are 
minute,  more  or  less  oval,  flattened  bodies,  of  a  soft  and  plasmic 


86 


GROWTH   AND    WORK   OF  PLANTS 


nature,  in  the  protoplasm.*    The  chlorophyll  is  a  green  pigment 
in  these  bodies  where  it  exists  in  numerous  very  fine  grains. 

The  chlorophyll  bodies  lie  in  the 
outer  layer  of  protoplasm,  next 
the  cell  wall.  They  are  distributed 
throughout  the  cells  of  the  loose 
parenchyma,  the  palisade  cells,  and 
the  guard  cells,  rarely  in  the  epider- 
mal cells  (they  occur  in  the  epidermis 
of  ferns)  and  are  absent  from  the 
vascular  bundles. 

2.   MODIFICATIONS   OF 
LEAVES. 

146.  The  normal  form  of  the 
leaf,  as  stated  in  the  previous 
chapter,  is  a  broad,  thin  organ 
which  thus  exposes  to  the  air  and 
light  a  great  surface  in  comparison 
with  its  bulk.  This  is  because 
the  normal  work  of  the  leaf  is 
most  advantageously  and  economi- 
cally carried  out  with  this  form. 
There  are,  however,  numerous  ex- 
ceptions to  this  form  presenting 
what  are  termed  modifications  of 
leaves  in  different  plants.  These 
modifications  are  shown  under  a 
variety  of  conditions:  first,  when 
the  leaf  has  entirely  lost  its  normal 
function;  second,  where  a  modification  is  demanded  to  enable  the 

*  Chromatophore  is  a  general  name  for  these  bodies.  They  are  capable  of 
division,  and  thus  grow  and  multiply  in  the  plant  as  the  cells  increase. 
When  devoid  of  color  they  are  leucoplasts,  when  they  have  the  chlorophyll 
green  they  are  chloroplasts,  when  they  have  red  or  yellow  pigments  they  are 
chromoplasts,  as  in  the  red  and  yellow  petals  of  flowers,  in  the  carrot,  etc. 


Fig.  76. 

Indian  pipe  plant  (Monotropa  uni- 
flora)  with  white  stems  and  white  scale 
leaves. 


LEA  VES  :   MODI  PICA  TIONS 


leaf  to  resist  the  trying  arid  climate  of  the  desert,  or  the  equally 
drying  air  of  arctic  or  alpine  regions;  third,  where  the  normal 
functions  of  the  leaf  are  combined  with  some  other  utility;  fourth, 
where  the  leaf  is  reduced  to  a  very  small  size  on  certain  parts  cf 
the  plant  devoted  to  other  than  the  vegetative  function  (on  the 
flower  shoot  for  example)  probably  according  to  the  law  of  cor- 
relation; fifth,  the  floral  leaves,  the  sepals  and  petals  of  the 
flower,  which  are  modified  leaves  with  usually  loss  of  chlorophyll, 
and  an  adaption  to  other  ends. 

147.  Modifications  where  the  normal  work  of  the  leaf  is 
lost. — First,  on   underground  stems   like  the    mandrake,  Solo- 
mon's seal,  the  wake  robin,  etc.,  the  leaves  are  reduced  to  mere 
scales,  are  colorless,  or  at  least  lack  the 

green    color.     The    annual   aerial    shoot 
bears  the  green  leaves.     Second,  in  cer- 
tain   parasitic    or   saprophytic    flowering 
plants,  like  beech  drops  (Epiphegus),  the 
Indian    pipe    (fig.    77),  etc.,  the   leaves, 
though  on  aerial  shoots,  lack  chlorophyll 
and  are  reduced  in  size  to  mere  scales, 
the    plant    obtaining    its    carbohydrate 
food   through    its    roots    from   its    host, 
or  as  a  saprophyte,  or  with  the  aid  of  a 
fungus  mycelium  in  its  roots.     Bud  scales 
show  another  modification  of  leaves  from 
the    normal    function.       Third,    in    the 
cacti'  the  leaves  are  supposed  to  be  re- 
duced to  mere  spines  since  the  stem  has 
taken  on  entirely  the  normal  function  of    foliage  leaves  is  developed, 
the  leaf.     But  in  the  barberry  the  leaves  of  the  main  shoots  are 
largely  in  the  form  of  three  rayed  spines.     That  these  are  leaves 
is  seen  from  their  position  on  the  stem  and  the  fact  that  there 
are  bud  and  shoots  in  their  axils. 

148.  Modifications  of  leaves  in  arid  or  arctic  regions. — 
The  leaf  is  greatly  reduced  in  area  so  that  there  is  a  small  amount 
of  surface  exposed  to  the   air  in  proportion  to   the  bulk  of  the 


88 


GROWTH   AND    WORK   OF  PLANTS 


leaf,  so  that  the  water  is  conserved.  These  leaves  often  closely 
overlap  or  lie  close  against  the  stem  as  scales.  The  cassiope 
(Cassiope  tetragona},  which  is  found  in  sphagnum  moors  in  some 
of  the  Northern  States,  and  is  common  from  Labrador  to  Green- 
land and  Alaska,  is  an  example. 

149.  Needle-like   leaves. — These  are   found  on  many  coni- 
fers,  especially  the   pines.     The   leaves  are   long,  narrow,   and 
thick,  and  are  called  needle  leaves.     They  have  a  thick,  waxy 
cuticle,  an  epidermis  with  thick  walls.     Beneath  the  epidermis 
there  are  several  layers  of  cells  the  walls  of  which  are  very  thick 
and  hard,  and  inside  is  the  mesophyll.     This  form  and  structure 
of  the  pine  leaves  enables  them  to  conserve  water  so  that  they 
lose  it  very  slowly;  otherwise  the  leaves  would  lose  so  much  water 
that  in  winter  the  trees  would  be  killed.    The  spruces  have  similar 
leaves,  but  they  are  shorter  and  more  flattened,  while  some  other 
evergreens  have  scale  leaves,  which  with  their  structure  enables 
them  to  endure  the  drying  effect  of  the  cold  winters. 

150.  Modifications  of  leaves  combining  the  normal  func- 
tions with   other   utilities.  —  First,   tendrils  and   tendrils   on 

leaves,  as  in  the  pea; 
also  where  the  petiole 
of  the  leaf  functions  as 
a  tendril,  as  in  the  vir- 
gin's bower  (Clematis}. 
Second,  the  leaves  of 
insectivorous  plants,  like 
the  Venus 's  flytrap,  the 
sundew  (see  paragraph 
138),  and  the  pitcher 
plants,  of  which  a  good 
example  is  the  com- 
mon pitcher  plant  of 
our  sphagnum  moors.  Here  the  leaf  is  modified  into  a  pitcher- 
shaped  structure,  broadened  near  the  middle  and  narrowed 
somewhat  near  the  free  end,  where  there  are  on  the  inside 
of  the  pitcher  numerous  bristle-like  hairs  pointing  downward. 


Fig.  78. 
Tendrils  of  sweet  pea  coiling  around  supports. 


LEAVES:   MODIFICATIONS 


89 


Certain  insects  which  enter  the  leaf 
from  crawling  out  by  these  hairs, 
they  fall  into  the  water  at  the 
pitcher  and  die. 

151.  Reduction  of  leaves  to 
on  the  flower  shoot. — Reduced 
flower  shoot  are  often  green,  small 
the  bell  flower,  marigold,  etc.  These 
bracts.  On  some  flower  shoots  the 
bracts  are  broad  and  colored  like 
the  petals  of  some  flowers  as  in  the 
flowering  dogwood.  Bracts  of  the 
flower  shoot  are  sometimes  termed 
sc.  les  when  they  are  more  or  less  rigid  and  thickened,  as  in  the 
heads  of  some  composites.  The  thickened  bases  of  the  scales 
on  the  flower  head  of  the  "  artichoke  "  (Cyanara  Scolymus)  are 
edible. 


are  prevented 
and  after  a  while 
bottom  of  the 

bracts  or  scales 

leaves  on  the 
and  thin,  as  in 
are  termed 


Fig.  79- 
Leaf  of  pitcher  plant  (Sarracenia). 


CHAPTER   XL 
WORK   OF   THE    LEAVES. 

152.  Work  performed  by  leaves. — There  are  several  kinds 
of  work  performed  by  the  leaves  which  we  will  study  as  follows : 
First,  Transpiration,  or  the  giving  off  of  water;    second,  Photo- 
synthesis, or  the  making  of  sugar  and  starch;   third,   Respiration, 
or  energesis,  the  energizing  of  the  plant,  which  results  in  waste; 
fourth,  Digestion,  the  preparation  and  transformation  of  foods; 
and  fifth,  Assimilation,  or  the  making  of  new  living  matter  and 
the  repair  of  waste.     Several  of  these  functions  are  carried  on  by 
all  parts  of  the  plant,  but  preeminently  by  the  leaves,  except  in 
those  plants  so  modified  that  some  other  plant  part  has  taken  on 
the  work  of  the  leaf,  as  in  the  cacti,  phylloclades,  etc. 

I.    TRANSPIRATION. 

153.  The  loss  of  water  by  leaves. — That  the  loss  of  water 
by  plants  is  chiefly  through  leaves  can  be  shown  by  an  interesting 


Fig.  80. 

After  a  few  hours'  drops  of  water  have  accumulated  on  the  inside  of  the 
jar  covering  the  leaves. 

experiment  as  follows.  A  few  fresh  leaves  are  cut  from  a  plant, 
and  the  ends  of  the  petioles  are  sealed  by  dipping  them  in  paraffin, 
These  are  now  placed  under  a  dry  bell  jar  or  inverted  fruit  jar, 

90 


WORK   OF    THE  LEAVES:    TRANSPIRATION 


and  a  similar  vessel  with  no  leaves  under  it  is  kept  as  a  check. 
In  the  course  of  an  hour  or  so  there  will  be  seen  a  film  of  mois- 
ture on  the  inside  of  the  glass  covering  the  leaves,  while  the 
other  glass  will  remain  dry.  The  moisture  came  from  the  leaves 
through  the  surface.  To  show  this  with  an  entire  plant,  the  pot 
and  soil  of  a  plant  with  a  goodly  number  of  leaves  are  covered 
with  rubber  cloth  to  prevent  the  escape  of  moisture  from  the  soil 
or  pot.  The  plant  is  now  covered  with  a  glass  bell  or  fruit  jar  so 
that  moisture  cannot  escape  below.  The  moisture  which  accu- 
mulates on  the  inside  of  the  glass  vessel  indicates  that  the  leaves 
in  their  normal  position  on  the  plant  give  off  water. 

154.  Form  in  which  the  water  escapes  from  the  plant.— 
This  can  be  shown  by  a  very  interesting  experiment.  A  plant  is 
covered  with  a  bell  jar  as  described  above,  and  at  the  same  time 
a  piece  of  cobalt  paper  *  pinned  to  a  stake  is  placed  under  the 
glass  vessel.  At  the  same  time 
another  piece  of  cobalt  paper 
is  placed  under  a  similar  dry 
glass  jar  with  no  plant  under 
as  shown  in  fig.  82.  The  co- 
balt paper  should  first  be  dried 
by  heat  so  that  it  is  blue.  In 
a  very  short  time  the  cobalt  Fte- 8l-  Fig- 82- 

j          ,1         •  .,1      ,1  Water  vapor        A  good  way  to  show  that 

paper    Under    the     jar    With    the     is  given  off  by     the  water  passes  off  from  the 

i  .11  i  11  1.1        the  leaves  when    leaves  in  the  form  of  water 

plant  will  begin  to  redden,  while   attached  to  the  vapor. 
the  paper  under  the  other  jar   condenPsesntinto 


paper  is  very  sensi- 
moisture in  the  air 
enough  moisture  has 
This  demonstrates 


is  still  blue.     The  blue  cobalt   on°the  SJ 

tive   to    moisture    and    a   little    coverfnghe  glthe 

will    quickly   redden   it   before    plal 

been  given   off   to   show   on  the  glass  jar. 

that  the  water  escapes   from  the   leaves  in  the   form  of  water 

*  Make  a  solution  of  cobalt  chloride  in  water.  Saturate  several  pieces 
of  filter  paper  with  it.  Allow  them  to  dry.  The  water  solution  of  cobalt 
chloride  is  red.  The  paper  is  also  red  when  it  is  moist,  but  when  it  is 
thoroughly  dry  it  is  blue.  It  is  very  sensitive  to  moisture  and  the  moisture 
of  the  air  is  often  sufficient  to  redden  it.  Before  using,  dry  the  paper  in  an 
oven  or  over  a  flame. 


92  GROWTH   AND    WORK   OF   PLANTS 


vapor.  When  a  sufficient  amount  of  water  vapor  is  given  off  by 
the  leaves  under  the  jar  it  condenses  on  the  cool  glass  in  the  form 
of  water.* 

155.  How  the  water  vapor  escapes  from  the  leaf. — The 
living  cells  of  the  leaf  contain  a  large  percentage  of  water  in  the 
cell  sap.     The  cell  walls  are  saturated  with  water  because  they 
imbibe  or  absorb  water  from  the  cells  which  they  bound.     In  the 
loose  parenchyma  of  the  leaf  (see  fig.  74)   there   are  numerous 
large  intercellular  spaces  containing  air.     The  water  on  the  sur- 
face of  these  cell  walls  is  in  contact  with  the  air.     This  water 
evaporates  -f  into  the  air  spaces,  or  passes  off  into  water  vapor. 
The  water  vapor  diffuses  in  the  intercellular  spaces,  so  that  the  air 
becomes  very  humid,  more  so  than  the  air  outside  of  the  leaf  on 
ordinarily  dry  days.     The  water  vapor  diffuses  out  of  the  leaf 
through  the  open  stomates,  and  makes  room  for  more  water  to 
evaporate  from  the  cell  wall.     The  cell  wall  in  turn  takes  by  imbi- 
bition more  water  from  the  cell,  so  that  under  conditions  favorable 
for  this  process  water  vapor  is  constantly  flowing  out  through  the 
stomates.     Some  water  also  evaporates  from  the  external  walls  of 
the  epidermal  cells,  but  the  quantity  is  usually  small  because  of 
the  waxy  cuticle  over  the  epidermis. 

156.  Conditions  which  favor  or  retard  transpiration.— 
Dry  air  favors  transpiration,  since  it  permits  a  more  rapid  diffusion 
of  the  water  vapor  out  of  the  intercellular  spaces.     Currents  of  air 
also  hasten  transpiration,  since  the  water  vapor  is  quickly  carried 
away  from  the  surface  of  the  leaf.     This  is  why  dry  winds  or  high 
winds  often  cause  plants  to  wilt,  especially  when  the  soil  is  dry  and 
absorption  by  the  roots  is  not  equal  to  the  transpiration  by  the 
leaves.     Light  also  favors  transpiration.     Since  osmotic  substances 
are  more  active  in  the  guard  cells,  they  become  turgid,  curve  back- 
ward and  keep  the  stomates  open.     Humid  air,  darkness,  or  weak 

*  A  good  illustration  of  the  condensation  of  water  vapor  on  the  surface 
of  a  cool  object  is  seen  in  the  summer  when  the  air  is  very  humid  and  drops 
of  water  accumulate  on  the  outside  of  a  pitcher  of  cold  water. 

f  If  it  is  desired  to  demonstrate  the  evaporation  of  water  a  shallow 
vessel  of  water  can  be  covered  with  a  bell  jar  or  tumbler.  The  condensa- 
tion of  water  on  the  inside  shows  some  of  the  water  has  evaporated. 


WORK   OF    THE   LEAVES:    TRANSPIRATION 


93 


light  retards  transpiration.  In  darkness  or  weak  light  the  stomates 
tend  to  close.  For  modifications  of  the  leaf  which  retard  the  loss 
of  water  see  paragraphs  148,  149. 


Fig.  83. 

Rhododendron  maximum  in  freezing  weather,  the  leaves  rolled  into  tubes  and 
hanging  directly  downward. 


157.  Whenever  possible  the  student  should  make  obser- 
vations on  the  loss  of  water  by  plants  and  the  effect  on  the  plant. 
This  can  be  done  sometimes  during  excursions.  Compare  the 
conditions  of  plants  in  very  dry  periods  in  dry  soil  with  the  same 
plants  during  a  moist  period.  Plants  grown  in  pots  *  or  small  boxes 
can  be  set  in  a  dry  room  and  left  without  watering;  some  can  be 
placed  where  there  are  dry  currents  of  air.  These  can  be  compared 
with  others  where  the  air  is  quiet  and  the  soil  is  kept  moist.  Plants 
with  thick,  leathery  leaves,  like  the  rubber  plant  or  the  purslane, 
can  be  set  in  a  dry  room  along  with  plants  with  thin  delicate  leaves 

*  The  pot  and  soil  should  be  sealed  hermetically  with  rubber  cloth  to 
prevent  evaporation  of  water. 


94 


GROWTH   AND    WORK   OF   PLANTS 


to  compare  the  result.  The  purslane  will  sometimes  grow  if  it  is 
hung  on  the  fence.  It  is  a  kind  difficult  to  kill.  Trees  and  shrubs 
with  thin  leaves  usually  shed  them  on  the  approach  of  winter, 
since  water  transpires  from  them  rapidly.  Evergreen  trees  have 
thick  and  hard  leaves  with  a  strong  cuticle.  They  lose  water 


Fig.  84. 

Rhododendron  maximum  during  mild  weather  in  the  winter,  leaves  expanded 
and  extending  out  laterally  in  normal  position. 


slowly.  Interesting  observations  can  be  made  on  rhododendrons, 
which  are  often  grown  in  city  parks  or  in  private  grounds.  In 
extremely  cold  weather  when  it  is  freezing,  the  rhododendron 
leaves  hang  downward  and  are  rolled  up  into  a  tube.  In  this 
way  the  leaves  lose  less  water  than  if  they  remained  flat.  It 
will  be  remembered  that  freezing  of  plant  tissue  has  a  drying 
effect. 


WORK   OF    THE   LEAVES:    TRANSPIRATION  95 

158.  How  drops  of  water  exude  from  leaves. — If  small, 
actively  growing  plants,  such  as  the  pea,  corn,  wheat,  bean,  etc.,  are 
put  under  a  bell  jar  and  placed  in  the  sunlight  where  the  tempera- 
ture is  suitable  for  growth,  in  a  few  hours,  if  conditions  are  favor- 
able, there  will  be  drops  of  water  standing  out  on  the  margins  of 
the  leaves.    These  drops  of  water  have  eluded  through  the  ordinary 
stomates,  or  in  other  cases  through  what  are  called  water  stomates, 
by  the  influence  of  root  pressure.     The  plant  being  covered  by 
the  bell  jar,  the  air  soon  becomes  saturated  with  moisture  and 
transpiration  is  checked.     Root  pressure  still  goes  on,  however, 
and  the  result  is  shown  in  the  exuding  drops.     Root  pressure  is 
here  in  excess  of  transpiration.*     This  phenomenon  is  often  to  be 
observed  during  the  summer  season  in  the  case  of  low-growing 
plants.     During  the  bright-  warm  day  transpiration  equals,  or  may 
be  in  excess  of,  root  pressure,  and  the  leaves  are  consequently 
limp  or  flaccid.     As  nightfall  comes  on  the  air  becomes  more  moist, 
and  the  conditions  of  light  are  such  also  that  transpiration  is 
lessened.     Root  pressure,  however,  is  still  active  because  the  soil 
is  still  warm.     In  these  cases,  drops  of  water  may  be  seen  exuding 
from  the  margins  of  the  leaves,  due  to  the  excess  of  root  pressure 
over  transpiration.     Were  it  not  for  this  provision  for  the  escape 
of  the  excess  of  water  raised  by  root  pressure,  serious  injury  by 
lesions,  as  a  result  of  the  great  pressure,  might  happen.     The  plant 
is  thus  to  some  extent  a  self -regulatory  piece  of  apparatus  so  far  as 
root  pressure  and  transpiration  are  concerned. 

159.  Number   of   stomates. — It   has  been  estimated  by  in- 
vestigation  that  in  general   there   are   40-300  stomates  to   the 
square    millimeter    of    surface.      In    some    plants    this    number 
is  exceeded,  as  in  the  olive,  where  there  are  625.     In  an  entire 
leaf  of   Brassica   rapa    there    are    about    11,000,000    stomates, 
a-nd  in  an  entire  leaf  of  the  sunflower  there  are  about  13,000,000 
stomates. 

160.  Amount  of  water  transpired  by  plants. — The  amount 
of  water  transpired  by  plants  is  very  great.     According  to  careful 

*  These  drops  should  be  distinguished  from  those  formed  merely  as  a 
result  of  condensation  of  moisture  on  the  leaves. 


96  GROWTH  AND    WORK   OF  PLANTS 


estimates,  a  sunflower  6  feet  high  transpires  on  the  average  about 
one  quart  per  day;  an  acre  of  cabbages  2,000,000  quarts  in  four 
months;  an  oak  tree  with  700,000  leaves  transpires  about  180 
gallons  of  water  per  day.  According  to  von  Hohnel,  a  beech  tree 
no  years  old  transpired  about  2250  gallons  of  water  in  one  sum- 
mer. A  hectare  of  such  trees  (about  400  on  2\  acres)  would  at 
the  same  rate  transpire  about  900,000  gallons,  or  about  30,000 
barrels  in  one  summer. 


CHAPTER   XII. 
WORK  OF    LEAVES    (Continued). 

II.    PHOTOSYNTHESIS. 

161.  The  formation  of  sugar  and  starch  during  photo- 
synthesis.— The    work    done   by   leaves   in   the   formation   of 
sugar  and  starch  requires  the  air  and  light  relations.*     In  the 
case  of  aquatic  plants  the  air  is  mixed  in  the  water  so  that  fun- 
damentally, so  far  as  the  process  is  concerned,  the  relations  of 
land  and  aquatic  plants  to  light  and  air  are  the  same,  though  it  is 
better  to  speak  of  the  light  and  water  relation  of  aquatic  plants. 
The  thin  and  broad  form  of  the  leaf  exposes  a  large  surface  to 
the  air  and  light,  while  the  stomates  and  intercellular  spaces  of 
the  leaf  afford  free  ccmmunication  of  air  into  the   mesophyll 
portion  of  the  leaf.     That  sugar  and  starch  are  plant  products 
we  have  learned  from  our  study  in  Chapters  I  and  II.     Now  we 
wish  to  learn  the  process  by  which  the  plant  makes  them. 

162.  Need  of  the  light  relation. — The  leaves  of   the   corn 
plant,  the  beet,  onion,  and  most  other  monocotyledons  which 
have  been  exposed  to  the  light  contain  a  certain  amount  of  sugar. 
On  the  other  hand  the  leaves  of  the  bean,  tropaeolum,  potato 
and  most  other  dicotyledons  which  have  been  exposed  to  the 
light  contain  starch,  which  can  be  demonstrated  by  dissolving 
out  the  chlorophyll  and  treating  the  leaf  with  a  tincture  of  iodine. 
A  small  quantity  of  sugar  is  also  present.     Starch  disappears  from 
leaves  which  have  been  kept  in  the  dark  during  the  night,  and  if  the 
leaf,  or  a  portion  of  it  be  kept  in  the  dark  the  following  day,  or 
in  very  weak  light,  no  starch  will  appear.     This  clearly  indicates 
that  light  plays  an  important  part  in  this  work  of  the  leaf  and 
explains  the  need  of  the  light  relation. 

*  In  the  case  of   aquatic  plants  the  relations  are  light  and  water,  the 
water  containing  air  mixed  with  it. 

97 


98  GROWTH   AND    WORK   OF  PLANTS 

163.  Need  of  the  air  relation  in  this  work  of  leaves.— 

The  air  relation  is  also  necessary  in  the  formation  of  sugar  and 
starch  as  well  as  in  respiration.  There  is  an  interchange  of 
gases  in  the  plant  during  the  process,  and  if  the  leaf  is  deprived 
of  one  of  the  necessary  gases  the  formation  of  sugar  and  starch 
ceases.  The  gas  which  the  plant  absorbs  during  this  process  is 
carbon  dioxide  (one  part  of  carbon  and  two  parts  of  oxygen  in 
the  molecule  of  carbon  dioxide  =  CO2).  The  air  consists  of 
about  twenty-one  parts  of  oxygen,  about  seventy-nine  parts  of 
nitrogen  and  a  small  fraction  of  one  part  of  CO2.  A  small  per- 
centage of  CO2  is  sufficient  since  during  respiration  of  animals 
and  plants,  and  by  the  burning  of  combustible  material,  CO2  is 
constantly  added  to  the  air.  More  than  about  4  per  cent  of  CO2 
in  the  air  is  harmful  to  most  plants.  While  CO2  is  absorbed  by 
plants  during  this  process  oxygen  is  given  off. 

164.  To  show  the  evolution  of  oxygen  by  green  plants. — 
For  a  simple  demonstration  of  the  oxygen  given  off  by  green 
plants,  water  plants  are  more  suitable  than  land  plants,  since 
the  gas  bubbles  can  easily  be  seen  as  they  rise  in  the  water. 
Nevertheless  with  proper  apparatus  and  methods  of  measuring 
and  determining  gases  it  can  be  demonstrated  that  the  same  gas 
(oxygen)  is  given  off  by  green  plants  in  the  air.     A  few  sprigs  of 
the  water  weed,  Elodea   (  =  Philotria),  with  freshly  cut  stems 
about  10  cm.   (4  inches)  long,  are  inverted  and  immersed  in  a 
bottle  of  spring  or  tap  water.     The  bottle  is  placed  in  the  sunlight. 
Bubbles  of  gas  will  soon  begin  to  rise  quite  rapidly  from  the 
cut  ends  of  the  stem.     If  the  bottle  is  moved  into  the  shade  for 
a  moment,  the  bubbles  are  given  off  very  slowly.     When  moved 
into  the  sunlight  again,  the  bubbles  immediately  begin  to  rise  at 
a  rapid  rate.     In  the  same  way  when  pond  scum  (threads  of  the 
alga,  Spirogyra,  for  example)  are  placed  in  a  vessel  of  spring  or 
tap  water  in  the  light,  the  bubbles  of  gas  are  given  off.     This  is 
interesting  as  indicating,  what  is  a  fact,  that  this  same  process 
takes  place  in  all  green  plants  which  have  chlorophyll. 

165.  To  determine  that  this  gas  is  oxygen. — A  large  quan- 
tity of  fresh  Elodea  is  placed  in  a  large  jar  of  tap  water.     A 


WORK  OF  LEAVES:   PHOTOSYNTHESIS 


99 


funnel  is  inverted  over  it,  leaving  a  few  sprigs  projecting  under 
the  edge  of  the  funnel  so  as  to  hold  the  edge  of  the  funnel  off  the 
bottom  of  the  jar  and  permit  a  free  circulation  of  water  and 
gases.  The  small  end  of  the  funnel  must  be  immersed.  A 
very  short  section  of  rubber  tubing  is  slipped  over  the  end  of 
the  funnel.  A  test  tube  is  filled  with  the  water,  inverted,  and 
the  open  end  immersed  so 
there  will  be  no  air  in  the 
tube.  It  is  then  slipped 
over  the  end  of  the  funnel 
and  squeezed  far  enough 
down  on  the  piece  of  rubber 
tubing  to  hold  it  firmly  in 
place.  The  apparatus  is  now 
placed  in  the  sunlight,  where 
it  will  receive  the  sun  during 
the  entire  day.  The  bub- 
bles of  gas  rise  into  the  test 
tube  and  displace  the  water.* 
When  the  tube  is  nearly  full 
of  gas  the  test  can  be  made. 
With  one  hand  the  tube  is 
removed,  at  the  same  time 
holding  the  thumb  over  the 
mouth  to  prevent  the  escape 
of  the  gas.  The  tube  is  now 
tipped  so  that  the  small 
amount  of  water  will  flow  to 
the  bottom.  A  soft  wood 
splinter  is  now  lighted.  After 
it  has  flamed  for  a  few  seconds  the  flame  is  extinguished  by 
blowing.  The  glowing  splinter  is  inserted  in  the  mouth  of  the 
tube.  It  flames  again.  This  indicates  that  the  gas  is  oxygen. 

*  The  water  should  be  changed  each  morning  until  the  tube  is  nearly 
full  of  gas.  To  do  this  slip  the  tube  off  the  funnel  into  a  tumbler  of  water. 
The  funnel  can  then  be  removed,  the  water  emptied  and  fresh  water  put  in 
the  jar.  The  tube  is  then  placed  in  position  again. 


Fig.  85. 
Apparatus  to  catch  oxygen  from  aquatic  plants. 


100 


GROWTH   AND    WORK   OF  PLANTS 


166.  To  show  that  C02  is  absorbed  while  0  is  given  off  by 
plants. — Boil  some  spring  water.  This  drives  off  the  air  and 
CO2  which  is  mixed  in  it.  When  the  water  is  cooled  a  few  sprigs 

of  Elodea  are  placed 
in  it  as  described  in 
paragraph  164.    It  is 
now    placed    in    the 
sunlight.     No  gas  is 
given  off.     If  oxygen 
is  added  by  thoroughly  agita- 
ting the  water  so  as  to  mix  air 
with  it,  and  it  is  placed  in  the 
sunlight,  no  gas  is  given  off. 
If    CO2   is    now    added    (by 
breathing    into    the    water 
through  a  glass  tube,  or  with 
a  gas   generator),   and   it   is 
placed  in  the  sunlight,  oxygen 
is  again  given  off. 

167.  A  chemical  change 
takes  place  in  the  gas  in 
the  cells  of  the  plant.— 
These  experiments  indicate  that  a  chemical  change  takes  place 
in  the  cells  of  the  plant,  for  if  a  simple  plant  like  the  pond  scums 
(Spirogyra)  is  used  the  result  will  be  the  same.  Since  sugar  and 
starch  are  formed  in  the  leaves  during  this  process,  they  are  a 
part  of  the  result  or  product  of  this  change. 

168.  How  this  change  takes  place  in  land  plants. — The 
chemical  change  which  takes  place  with  aquatic  plants,  as  indi- 
cated by  our  experiments,  occurs  also  in  the  case  of  the  green 
land  plants.  The  air  is  a  mixture  of  a  number  of  gases.  The 
principal  and  constant  gases  in  the  air  mixture  are  as  follows. 
In  every  100  parts  there  are  about  21  parts  of  oxygen  (symbol 
for  oxygen  =  O),  about  79  parts  of  nitrogen  (symbol  for  nitro- 
gen =  N),  and  a  very  small  fraction  of  carbon  dioxide  (symbol 
for  carbon  dioxide  =  CO2).  The  latter  gas  is  a  very  poisonous 


Fig.  86. 
Ready  to  see  what  the  gas  is. 


WORK   OF   LEAVES:   PHOTOSYNTJlttST.±  IOL 


one,  or  rather  suffocating  gas.  We  have  'ajr^ad^  .  no&ed '  iii*tf 
carbon  dioxide  is  easily  absorbed  by  water.  Water  is  a  com- 
pound of  two  gases,  hydrogen  two  parts  and  oxygen  one  part, 
and  the  symbol  for  water 
is  therefore  H2O.  The 
land  plants  absorb*  some 
of  the  carbon  dioxide  from 
the  air,  and  it  is  also  Fig.  87. 

-  ,         .  ,  .          ,  The  splinter  lights  again  in  the  presence  of 

formed   within    the    plant       oxygen  gas. 

cells  of  all  plants  during  respiration.     But  whether  formed  in 

the   plant  cell  or  absorbed  from   the  air,  as   soon  as  it  comes 

in   contact   with  the  water  in  the  cell  it   is  absorbed.      When 

carbon   dioxide    is  absorbed  by  water,  the  two   together  form 

carbonic  acid  (CO2  +  H2O  =  CH2O3  =  the  symbol  for  carbonic 

acid).f 

169.  There  are  five  principal  requirements  in  the  process 
of  photosynthesis!  during  which  the  formation  of  starch  and 
sugar  in  green  plants  takes  place.  First,  the  living  plant  cell; 
second,  the  presence  of  carbonic  acid;  third,  the  presence  of  chloro- 

*  The  process  of  transpiration  keeps  the  cell  wall  saturated  with  water. 
This  provides  the  water  for  the  solution  of  the  CO2  which  in  the  dry  con- 
dition (anhydride  condition)  could  not  diffuse  through  a  dry  cell  wall  fast 
enough.  This  is  believed  to  be  one  of  the  important  functions  of  trans- 
piration. In  the  case  of  aquatic  plants  the  CO2  in  the  water  is  dissolved 
and  is  therefore  CH2O3  =  carbonic  acid. 

t  In  the  case  of  aquatic  plants  the  water  in  which  they  grow  absorbs 
carbon  dioxide  from  the  air,  thus  forming  the  carbonic  acid  which  they 
absorb  from  the  water. 

I  It  is  now  evident  what  photosynthesis  means.  The  first  part  of  the 
word  comes  from  the  Greek  word  0orr6s  =  light,  and  the  last  part  of  the 
word  has  reference  to  the  synthetic  process,  or  union,  or  putting  together. 
The  process  was  formerly  considered  a  process  of  assimilation  and  was 
called  carbon  dioxide  assimilation.  True  assimilation,  however,  is  brought 
about  entirely  by  the  living  substance  of  the  plant  (see  paragraph  176). 
In  "carbon  dioxide  assimilation"  sunlight  supplies  the  energy  for  one  step 
in  the  process,  and  it  seems  better  to  use  the  term  photosynthesis,  though 
if  the  nature  of  the  process  is  kept  clearly  in  mind  there  should  be  no  very 
great  objection  to  saying  carbon  dioxide  assimilation.  Some  use  the  term 
fixation  of  carbon. 


-102  GROWTH  AND    WORK   OF  PLANTS 

pay}.].;  fqu/tfo  ,  sunlight  shining  into  the  cell;  fifth,  the  chemical 
changes.  The  chlorophyll  absorbs  some  of  the  rays  of  light  and 
this  furnishes  the  power,  we  might  say,  to  break  up  the  carbonic 
acid  compound  in  such  a  way  as  to  separate  its  elements.  But 
according  to  chemical  laws  these  elements  cannot  long  remain 
separated  under  these  conditions.  They  quickly  unite  into  other 
compounds  or  into  a  different  compound.  The  different  steps 
in  the  process  are  very  complicated  and  some  of  them  are  not  well 
known.  But  the  first  compound  which  we  can  definitely  recog- 
nize in  the  plant  as  a  result  of  this  chemical  change  is  the  substance 
sugar*  The  symbol  for  grape  sugar  is  C6H12O6,  because  one 
molecule  of  sugar  contains  6  parts  of  carbon,  12  parts  of  hydrogen 
and  10  parts  of  oxygen.  In  the  making  of  one  molecule  of  sugar, 
therefore,  6  molecules  of  the  carbonic  acid  are  necessary  as  will  be 
seen  by  the  following  simple  mathematical  formula,  6(CH2O3)  = 
C8H12O18.  Now  subtract  the  sugar  symbol  from  this  as  follows, 
C6H12O18  —  C0H12O6  =  i20;  i.e.,  there  are  12  molecules  of  pure 
oxygen  set  free  in  the  plant  cell  which  the  plant  cannot  use  in  this 
process.  Much  of  this  pure  oxygen  escapes  by  way  of  the  sto- 
mates  into  the  open  air  again.  It  is  an  interesting  fact  that  during 
this  process  by  which  sugar  is  made  in  plants,  pure  oxygen  is 
added  to  the  air  and  thus  in  general  the  proper  balance  or  pro- 
portion of  this  gas  is  maintained;  otherwise,  the  air  wrould  in  time 
become  so  depleted  in  oxygen  that  it  could  not  sustain  animal 
life,  since  animals  use  oxygen  of  the  air  in  respiration.  It  is  also 
interesting  to  note  that,  in  this  process,  the  green  plants  use 
carbon  dioxide  from  the  air,  which  animals  give  off  during  res- 
piration. Green  plants,  therefore,  in  this  respect,  as  well  as  in 
so  many  others,  perform  a  very  important  work  in  nature. 

170.  How  starch  is  formed  from  sugar. — Sugar  is  changed 
to  starch  in  the  plant  by  the  loss  of  one  molecule  of  water.     The 

*  It  is  interesting  to  note  that  the  proportion  of  hydrogen  and  oxygen  in 
the  sugar  compound  is  the  same  as  that  of  a  molecule  of  water,  i.e.,  H2O. 
The  same  is  true  of  most  sugars,  and  of  starch.  Those  compounds  of  car- 
bon, hydrogen  and  oxygen  which  contain  the  H  and  O  in  the  proportion 
,  are  known  as  carbohydrates. 


WORK  OF  LEAVES:   PHOTOSYNTHESIS  103 

result  can  be  seen  from  the  following  simple  formula:  Grape 
sugar,  C6H12O6  —  H2O  =  C8H10O5,*  which  is  the  symbol  for 
starch.  In  many  plants  the  sugar  formed  in  the  leaves  does  not 
change  to  starch  except  that  which  is  stored  in  the  seed,  as  in  field 
corn,  wheat,  barley,  etc.  Sugar  is  found  throughout  other  parts 
of  the  plant,  and  we  have  seen  that  it  is  stored  in  quantity  in  the 
sugar  beet.  In  some  plants  it  is  not  even  changed  to  starch  in 
the  seed,  as  in  the  sweet  corn.  In  many  plants,  however,  it  is 
changed  to  starch  in  the  leaf  very  soon  after  its  formation  in  the 
leaf,  as  in  most  dicotyledons. 

171.  Where  the  starch  grains  are  first  formed. — The  sugar 
is  dissolved  in  the  cell  sap,  but  the  starch  is  deposited  in  grains. 
These  grains  of  starch  at  the  time  of  their  formation  are  deposited 
in  the  chlorophyll  bodies.     Each  grain  begins  as  a  very  small  body 
and  increases  in  size.     (For  translocation  and  storage  of  starch, 
see  Chapter  XIV.) 

172.  Photosynthesis  takes  place  only  in  chlorophyll-bear- 
ing plants  and  in  the  chlorophyll-bearing  parts. — Plants  which 
have  been  grown  in  the  dark  lack  chlorophyll,  f    When  brought 
into  the  light  photosynthesis  does  not  take  place  until  chlorophyll 
has  been  formed.     So  in  variegated  leaves,  photosynthesis  does 
not  take  place  in  the  white  portions  because  chlorophyll  is  absent, 
but  it  does  take  place  in  the  green  parts  of  such  leaves  or  in  such 
parts  as  have  chlorophyll.     Photosynthesis  does  not,  therefore, 
take  place  in  the  roots,  not  even  in  the  roots  of  green  plants,  nor 
in  stems  where  chlorophyll  is  not  present.     Experiments  with 
chlorophyll-less  plants  like  beech  drops  (Epiphegus),  the  Indian 
pipe  (Monotropa},  and  the  fungi  and  bacteria  $  show  that  photo - 

*  The  symbol  for  starch  is  probably  some  multiple  of  this  and  is  usually 
written  (C6H10O5)N. 

f  There  are  some  few  exceptions.  The  first  leaves  of  pine  seedlings  have 
chlorophyll  leaves  even  grown  in  the  dark. 

t  A  few  bacteria,  however,  are  known  to  be  able  to  form  their  own  car- 
bohydrates. The  nitrite  and  nitrate  bacteria  which  convert  ammonia  com- 
pounds into  nitrites  and  nitrates  in  the  soil  obtain  energy  from  the  chemical 
process  of  making  nitrites  and  nitrates,  so  that  they  can  assimilate  the  CO2 
of  the  air.  This  is  not  photosynthesis  however,  since  light  does  not  supply 
the  energy.  It  is  chemo synthesis. 


104  GROWTH  AND   WORK  OF  PLANTS 

synthesis  cannot  take  place  in  them.  They  are  dependent  for 
their  carbohydrate  food  on  green  plants.*  They  obtain  it  either 
as  parasites  on  living  green  plants,  or  by  growing  on  their  dead  or 
disintegrated  remains  as  saprophytes;  or  on  other  plants  or  animals 
which  in  their  turn  are  dependent  on  the  green  plants  primarily 
for  their  carbohydrate  food. 

173.  Conditions  favoring  photosynthesis. — From  the  pre- 
ceding experiments  and  discussion  it  is  clear  that  light  and  air,  the 
chlorophyll,  and  the  living  substance  of  the  plant,  are  essential  to 
the  formation  of  sugar  and  starch.     But  the  rapidity  of  their  for- 
mation is  influenced  by  the  varying  intensity  of  light,  tempera- 
ture, and  the  percentage  of  CO2  in  the  air.f 

174.  Amount  of  carbohydrates  formed. — According  to  some 
experiments  by  Sachs,  t  the  increase  in  dry  substance  of  leaves  of 
a  sunflower  or  squash  was  about  20  grams  per  day  of  twelve  hours 
on  bright,  warm  days,  for  one  square  meter  of  leaf  surface.     He 
estimates  that  on  a  warm,  bright  day  a  vigorous  sunflower  would 
make  an  increase  in  dry  weight  of  about  36  grams,  and  a  squash 

*  In  using  the  term  green  plants  here,  the  chlorophyll-bearing  plants 
are  understood.  It  should  be  remembered  that  there  are  green  plants, 
especially  among  the  fungi,  which  do  not  possess  chlorophyll. 

f  The  products  of  photosynthesis  increase,  other  things  being  equal, 
with  an  increase  of  CO2  from  the  normal  (about  .05  part  in  100  of  air)  up 
to  4  per  cent  (4  parts  to  100),  but  a  larger  increase  in  the  CO2  acts  injuriously 
to  the  plant.  With  suitable  temperature  conditions,  the  products  of  photo- 
synthesis increase  with  the  increase  of  the  intensity  of  light,  from  very  weak 
light  where  photosynthesis  is  feeble,  to  the  brightest  sunlight  whexc  it  reaches 
its  highest  intensity.  Temperature  also  influences  the  rate  of  photosyn- 
thesis. At  low  temperatures  it  is  feeble  or  nil,  and  increases  up  to  25°  C.- 
40°  C.  (77°  F.-io4°  F.)  where  it  reaches  its  highest  intensity,  and  with  higher 
temperatures  soon  ceases.  Photosynthesis  also  takes  place  at  quite  low  tem- 
peratures even  several  degrees  below  freezing.  Photosynthesis  continues  in 
winter  mostly  in  evergreens  at  freezing  or  even  a  few  degrees  below,  but  quite 
low  temperatures  bring  about  inactivity  of  the  chlorophyll  bodies.  The 
number  and  distribution  of  stomates  also  conditions  the  rate  of  photosyn- 
thesis since  the  diffusion  of  gases  is  dependent  on  them.  When  the  plants 
are  quite  dry  the  rate  is  less  than  when  the  leaves  are  well  supplied  with 
water,  other  things  being  equal. 

J  Arb.  bot.  Inst.  Wlirzburg,  3,  1884. 


WORK  OF  LEAVES:   ASSIMILATION  10$ 

about  185  grams  dry  substance.  This  included  other  things  than 
starch.  Brown  and  Morris  *  estimate  that  in  one  day  (twelve 
hours)  one  square  meter  of  leaf  surface  of  the  sunflower  will 
make  about  8£  grams  of  carbohydrates  of  which  the  larger  part  is 
sugar,  the  smaller  part  starch.  This  would  make,  on  the  same 
estimates  as  above,  about  15-20  grams  of  carbohydrate  as  the 
result  of  one  day's  work  of  a  vigorous  sunflower  on  a  warm, 
bright  day. 

175.  Amount  of  C02  use(f  during  photosynthesis. — Large 
quantities  of  CO2  are  used  in  photosynthesis.     A  sunflower  plant 
uses  about  50  grams  CO2  per  day  (=  nearly  2  oz.).     Supposing 
the  earth  were  covered  with  sunflowers  it  has  been  estimated  that 
they  would  consume  135,000,000,000  kilograms  (=  297,000,000,- 
ooo  Ibs.).     The  amount  of  CO2  in  the  air,  if  not  replenished,  at 
this  rate  would  last  the  sunflowers  about  twenty  months.     This 
estimate  is  perhaps  excessive.     Another  estimate  is  that  a  hectare 
(2^  acres)  of  forest  would  consume  11,000  kg.   (=  24,200  Ibs.) 
CO2  per  year.     This  large  amount  of  CO2  is  being  continually 
restored  to  the  air  by  the  burning  of  wood,  coal,  etc.,  for  food,  and 
by  the  respiration  of  animals  so  that  the  normal  balance  is  main- 
tained.    The  celebrated  Krupp  works  for  the  manufacture  of 
ordnance  at  Essen,  Germany,  alone  produces  about  2,500,000  kg. 
(=  5,500,000  Ibs.)  CO2  per  day.     It  is  estimated  that  the  human 
beings  of  the  earth  give  back  to  the  air  about  12,000,000  kg. 
(26,400,000  Ibs.)  CO2  each  day.f 

III.   ASSIMILATION. 

176.  The  term  assimilation  usually  has  a  wider  applica- 
tion by  students  of  plants  than  by  students  of  animals. — 

Assimilation  in  animals  is  the  building  up  of  new  living  matter 
and  structures  of  the  body,  while  in  plants  it  has  been  customary 
to  use  the  word  assimilation  not  only  for  the  building  up  of  new 
living  substance  and  new  structures  of  the  organism,  but  also  for 

*  Journal  Chem.  Soc.,  63  (Transact.),  604.  See  Jost,  Pflanzenphysiolo- 
gie,  140,  1904;  p.  114,  Engl.  Ed.,  1907. 

t  See  "Text  Book  of  Botany,"  Strasburger,  Noll,  etc.,  196,  English 
edition. 


106  GROWTH   AND    WORK   OF   PLANTS 

the  formation  of  food  products  which  are  later  used  by  the  plant 
and  are  also  used  as  food  by  animals.  There  is  a  tendency  in 
recent  years  on  the  part  of  some  botanists  to  distinguish  the  kinds 
of  assimilation.  Those  kinds  of  assimilation  which  relate  to  the 
making  of  the  new  life  substance,  or  the  making  of  structures 
which  are  part  of  the  living  organism,  are  looked  upon  as  true 
assimilation.  Those  processes  which  result  in  making  food 
products  are  called  synthetic  assimilation.  The  making  of  sugar 
and  starch  (carbohydrates)  is  called  photo  synthetic  assimilation, 
because  the  sun  supplies  the  energy  for  the  initial  stages  in  the 
process.  The  making  of  carbohydrates  by  the  nitrite  and  nitrate 
bacteria  is  called  chemo synthetic  assimilation,  because  the  chemi- 
cal process  or  metabolism  in  changing  ammonia  compounds  to 
nitrites  and  these  into  nitrates  by  these  bacteria,  gives  them  the 
energy  to  fix  the  carbon  from  the  CO2. 

177.  Metabolism. — Metabolism  means  change,  or  changing 
around,  and  in  the  life  processes  of  animals  and  plants  refers  to  the 
chemical  changes  taking  place.     The  building  up  processes,  the 
different  kinds  of  assimilation,  are  constructive  metabolism  (an- 
abolism),  while  the  breaking  down  processes,  respiration,  fermen- 
tation, decay,  etc.,  are  destructive  metabolism  (katabolism). 

178.  The  building  up  of  proteids  in  the  plant. — The  proteid 
substances  in  plants  have  a  more  complicated  molecule  than  the 
carbohydrates  since  they  contain  C,  H,  O,  N,  S  and  sometimes  P. 
These  are  largely  formed  in  the  leaf,  but  are  formed  in  other  parts 
of  the  plant  also,  and  perhaps  can  be  formed  in  limited  extent  in 
any  living  plant  cell.     Some  plant  physiologists  claim  that  they 
are  formed  only  in  sunlight  and  in  the  presence  of  chlorophyll.* 

*  One  reason  for  this  belief  is  that  in  some  plants  it  has  been  found 
that  the  nitrates  (salts  of  nitric  acid  =  HNO3)  which  are  absorbed  by  the 
roots  accumulate  in  the  leaves  during  the  night,  and  disappear  during  the 
day.  During  the  day  the  nitrates  unite  with  carbohydrates  (sugar)  and 
some  sulphur  compounds  to  form  proteids.  Those  who  believe  that  pro- 
teids are  also  formed  during  the  night  concede  that  they  are  formed  more 
actively  during  the  day  because  photosynthesis  is  then  going  on,  since  the 
formation  of  carbohydrates  is  then  active  and  in  their  elemental  condition 
may  more  easily  unite  with  the  nitrates. 


WORK  OF  LEAVES:  DIGESTION         IO/ 

179.  The  leaf  as  the  organ  of  assimilation. — The  formation 
of  carbohydrates,  the  proteids  and  some  other  substances,  while 
taking  place  in  all  green  parts  of  plants,  is  predominant  in  the  leaf 
because  of  its  adaptation  %to  the  process  of  photosynthesis,  and  the 
close  relation  of  the  formation  of  other  products  closely  dependent 
on  the  carbohydrates.     The  sulphates,  phosphates,  nitrates,  etc., 
absorbed  by  the  roots  meet  the  carbohydrates  in  the  leaf  and  are 
here  assimilated. 

IV.   DIGESTION.* 

180.  Digestion  in  plants  includes  those  processes  in  which 
food  products  and  food  substances  either  in  the  plant  or  outside 
of  it  are  changed  chemically  into  a  condition  in  which  they  can  be 
assimilated  into  new  life  substance  or  plant  structures,  or  trans- 
ported to  other  parts  of  the  plant,  or  absorbed  from  the  outside 
if  they  are  not  already  in  a  condition  to  be  absorbed  (the  action  of 
roots  on  insoluble  solutions  in  soil,  and  the  action  of  ferments  on 
insects  in  case  of  carnivorous   plants,  paragraph  38).     Several 
kinds  of  digestion  are  performed  by  leaves  (digestion  of  insects 
by  carnivorous  plants  is  one   example).     One   special  kind  of 
digestion  occurring  in  the  leaf  is  the  digestion  of  starch.     The 
starch  formed  in  the  leaf  cannot  be  used  for  food  by  the  grow- 
ing leaf  nor  can  it  be  transported  to  other  parts  of  the  plant  until 
it  is  dissolved.     The  starch  is  dissolved,  or  digested,  in  the  leaf 
by  a  special  substance,  leaf  diastase,  which  is  formed  by  the  leaf 
for  this  purpose.     It  is  active  at  night,  so  that  the  starch  formed 
in  the  leaf  during  the  day  is  changed  to  a  sugar  at  night,  and  then 
flows  to  other  parts  of  the  plant  where  it  is  assimilated  by  growing 
organs,  or  is  stored  as  reserve  starch  in  seeds,  stems,  roots,  tubers, 
etc.     For  a  discussion  of  diastase,  see  paragraph  219. 

*  See  also  Chapter  XVI. 


CHAPTER   XIII. 
WORK    OF    LEAVES    (Concluded). 

V.    RESPIRATION. 

181.  The  leaves  are  also  organs  for  respiration,  but  since 
respiration  takes  place  in  all  growing  parts  of  plants  the  subject 
will  here  be  treated  with  reference  to  plants  in  general. 

182.  How  seedlings  breathe. — Plants  breathe  just  as  truly 
as  animals  do,  though  they  do  not  have  lungs.     Breathing,  in 
animals  as  in  plants,  is  the  taking  in  of  a  gas,  oxygen,  into  the 
body,  and  giving  off,  or  excreting  another  kind  of  gas,  carbon 
dioxide.     That  germinating  seeds  give  off  carbon  dioxide  can  be 
shown  in  the  following  way.     A  quart  of  peas  which  have  been 
soaked  in  water  for  twelve  or  fifteen  hours,  are  placed,  without 
any  water,  in  two  fruit  jars  or  two  large  wide -mouthed  bottles, 
which  are  then  closed  tightly.     Another  jar  or  bottle  empty  but 
closed  tightly  is  kept  as  a  check.     In  twenty-four  hours  let  us 
pour  a  small  quantity  of  barium  hydrate*  down  the  inside  of  the 
jar  or  bottle,  and  close  the  bottle  quickly  again.     A  white  pre- 
cipitate f  is  formed.     If  the  bottle  is  opened  again  and  tipped  so 
as  to  pour  some  of  the  gas  into  an  open  vessel  with  a  little  barium 
hydrate,  the  white  precipitate  appears  in  the  vessel  of  baryta 
water.     The  gas  is  heavier  than  air  and  is  easily  poured  into  the 
baryta  water.     If  some  of  the  barium  hydrate  is  poured  into  the 
empty  bottle,   no   precipitate   is  formed  or  only   a  very  small 
quantity. 

Now  in  the  other  bottle  the  lighted  end  of  a  splinter  or  taper 
may  be  lowered.     The   flame  is  immediately  extinguished  be- 


*  To  make  barium  hydrate.     Dissolve  barium  oxide  in  water. 
and  keep  in  a  tightly  corked  bottle, 
f  This  is  barium  carbonate,  BaCO3. 

108 


Filter 


WORK   OF  LEAVES:   RESPIRATION  ICX) 

cause  of  the  presence  of  a  suffocating  gas,  carbon  dioxide.  If 
the  lighted  end  of  a  splinter  or  taper  is  placed  in  the  empty 
bottle  it  is  not  extinguished  soon  because  the  suffocating  gas 
was  not  present.*  In  time,  however,  it  may  be  extinguished 
owing  to  the  accumulation  of  the  CO2  from  the  burning  splinter. 

This  experiment  teaches  us  that  the  suffocating  gas  (carbon 
dioxide)  is  given  off  in  quantity  by  the  peas  during  germination. 
That  it  is  carbon  dioxide  is  shown  by  the  white  precipitate  when 
the  barium  hydrate  is  poured  down  the  inside  of  the  bottle. 
Some  of  the  element  barium  unites  with  some  of  the  carbon 
dioxide  by  chemical  change  and  forms  barium  carbonate,  which 
is  the  white  precipitate. 

In  this  experiment  care  must  be  taken  to  test  with  the  barium 
hydrate  before  holding  the  flame  in  the  bottle  of  peas.  It  is 
much  better  to  have  a  separate  bottle  of  peas  for  the  test  with 
the  flame.  This  is  because  carbon  dioxide  is  formed  during 
the  burning  of  the  splinter.  To  prove  this  pour  some  barium 
hydrate  down  the  inside  of  the  empty  bottle  after  the  flame  has 
been  held  in  it.  To  show  that  animals  also  exhale  carbon  dioxide 
while  they  breathe,  take  a  shallow  vessel  of  baryta  water  and 
breathe  on  it  several  times.  A  thin  film  of  the  white  precipitate 
(barium  carbonate)  is  formed  on  the  surface  of  the  barium 
hydrate,  f 

183 .  The  germinating  seeds  take  oxygen  gas  from  the  air 
while  they  breathe. — A  simple  experiment  will  show  this.  A 
handful  of  wheat  is  soaked  in  water,  and  then  placed  in  a  germi- 
nator  (a  moist  vessel)  in  the  folds  of  a  wet  cloth.  When  it  has 

*  The  extinguishing  of  the  flame  does  not  prove  that  CO2  is  present. 
That  has  been  proven  by  the  former  experiment,  and  since  we  know  by  this 
that  CO2  is  present  it  is  fair  to  conclude  that  this  is  the  gas  in  this  instance 
which  extinguishes  the  flame. 

t  Lime  water  may  be  used  instead  of  baryta  water  for  all  the  above  ex- 
periments, but  it  is  not  so  satisfactory  as  baryta  water  because  the  result  is 
not  so  striking.  To  make  lime  water  place  a  lump  of  lime  twice  as  large 
as  a  hen's  egg  in  a  quart  of  water.  Allow  it  to  settle  and  in  a  day  or  two  filter 
the  liquid  and  keep  corked  tightly  in  a  bottle.  .  The  white  substance  formed 
when  lime  water  is  used  is  calcium  carbonate,  or  carbonate  of  lime. 


no 


GROWTH   AND    WORK  OF  PLANTS 


begun  to  sprout  the  bulbs  of  two  thistle  tubes  are  filled  with  the 
sprouted  grains.  A  piece  of  sphagnum  moss,  or  loose  cotton, 
can  be  placed  in  the  lower  part  of  the  bulb  to  prevent  the  grains 
from  falling  down  the  tube.  The  tubes  may  be  supported  as 

^___ shown   in  fig.    88,  with  the   small 

ends,  one  in  a  vessel  containing  a 
strong  solution  of  barium  hydrate, 
and  the  other  in  a  vessel  contain- 
ing a  strong  solution  of  caustic 
potash  (one  stick  of  caustic  potash 
in  two-thirds  tumbler  of  water). 
Red  ink,  or  some  red  analine  dye, 
may  be  added  to  the  solution  to 
make  the  liquid  visible  as  it  rises 
in  the  tube.  Each  bulb  is  closed 
airtight  by  a  piece  of  glass  cemented 
down  with  vaseline  of  sufficient 
consistency.  If  the  experiment  is 
properly  set  up,  in  twelve  to  twenty- 
four  hours  the  liquid  will  be  seen 
to  be  rising  in  the  tubes. 

184.  Why  the  liquid  rises  in 
the  tubes. —  From  the  experiment 
with  the  germinating  peas  we  know  that  barium  hydrate 
absorbs  carbon  dioxide.  The  potash  solution  also  absorbs 
carbon  dioxide.  The  germinating  wheat  during  respiration,  i.e., 
while  it  breathes,  gives  off  carbon  dioxide  just  as  the  peas  do. 
The  carbon  dioxide  being  heavier  than  the  air  settles  down  in 
the  tube  and  comes  in  contact  with  the  potash  solution  and  is 
absorbed.  Now  at  the  beginning  of  the  experiment  the  thistle 
tube,  and  the  space  between  the  wheat  grains,  was  filled  with  air. 
If  no  portion  of  the  air  was  taken  from  the  tube  the  liquid  could 
not  rise  as  the  carbon  dioxide  is  absorbed.  This  experiment 
proves  then  that  some  constituent  of  the  air  is  absorbed  by  the 
germinating  wheat  grains  and  undergoes  a  chemical  change  in 
the  wheat  seedlings. 


Fig.  88. 

Apparatus  to  show  respiration  of  ger- 
minating wheat. 


WORK  OF  LEAVES:  RESPIRATION  III 

185.  Oxygen  is  absorbed  by  the   germinating  wheat.— 

The  constituent  of  the  air*  which  is  removed  under  these  con- 
ditions is  one  which,  on  undergoing  a  chemical  change  in  the 
germinating  wheat,  unites  with  some  element  in  the  wheat  to 
form  the  carbon  dioxide  given  off.  From  the  abundance  of 
carbon  dioxide  given  off  it  is  plain  that  the  carbon  is  the  element 
in  the  wheat  with  which  the  constituent  absorbed  from  the  air 
unites.  Nitrogen,  it  is  plain,  cannot  unite  with  the  carbon  to 
form  carbon  dioxide.  It  must  then  be  the  oxygen  from  the  air 
which  is  absorbed  by  the  wheat,  and  which  unites  with  the  car- 
bon in  the  wheat  to  form  the  carbon  dioxide  given  off.  The 
oxygen  absorbed  by  the  germinating  seeds  unites  to  form  some 
of  the  substance  of  the  seedlings,  and  the  carbon  and  oxygen 
which  unite  to  form  the  carbon  dioxide  come  from  the  sub- 
stance of  the  seedlings.  The  oxygen  absorbed  then  replaces  that 
which  is  given  off  as  a  waste  product  in  the  carbon  dioxide. 
The  rising  of  the  potash  or  barium  hydrate  solution  in  the  tube 
in  this  experiment  indicates  to  us  then  that  oxygen  is  taken  from 
the  air  during  the  respiration  of  the  seeds.  This  is  exactly 
what  takes  place  when  we  breathe,  or  in  animal  respiration. 
Oxygen  is  inhaled  and  carbon  dioxide  is  exhaled. 

186.  Respiration  in  opening  leaf  buds  or  flower  buds. — 
Leaf  buds  or  flower  buds  are  excellent  objects  to  use  in  showing 
the  excretion  of  carbon  dioxide.     If  a  handful  of   the  buds  is 
placed  in  a  jar  as  described  in  paragraph  182   for  the  germin- 
ating peas,  in   the  course  of  ten  to  twelve  hours  they  will  be 
ready  for   the  test  with   the   barium   hydrate    and   the    lighted 
splinter  or  taper.      The  buds  can  be  obtained  throughout  the 
spring,  summer  and  autumn  in  the  open,  and  during  the  winter 
in  greenhouses. 

187.  Leaves  as    organs  of    respiration. — The    leaves    are 
organs  of  respiration.     The  stomates  provide  the  openings  for 
the  interchange  of  gases.     The  gases  diffuse  through  the  inter- 
cellular spaces  and  reach  all  parts  of  the  leaf.     The  gas  entering 

*  See  paragraph  168,  where  the  constituents  are  given  as  oxygen,  nitro- 
gen, and  carbon  dioxide. 


112  GROWTH  AND    WORK   OF  PLANTS 

the  leaves  is  also  diffused  to  other  parts  of  the  plant,  the  grow- 
ing buds,  and  also  parts  of  the  stem.  Some  succulent  stems 
are  provided  with  stomates  also,  and  the  stems  of  shrubs  and 
trees  are  provided  with  openings  called  lenticels  through  which 
there  is  an  exchange  of  gases. 

188.  Conditions   of   respiration. — Light  does   not  exercise 
any  important  influence  on  respiration,  but  warmth  is  of  fun- 
damental  significance.      The    minimum   temperature    at  which 
respiration   takes    place    is    a    little    below    the    freezing    point 
(o°  C.  =  32°  F.)  in  most  plants  but  it  has  been  shown  to  be  as 
low  as  —  10°  C.     As  temperature  increases  the  intensity  of  res- 
piration increases  up  to   a  maximum  intensity,  which   in  most 
plants  is  injurious  to  the  other  life  processes,  and  then  the  in- 
tensity decreases.     The  optimum  temperature  for  respiration  is 
below  the  maximum,  and  is  the  highest  temperature   at  which 
the  other  life  processes  are  not  injured.     This  varies  for  differ- 
ent plants.     Water   has   no   specific   influence,    but   affects   the 
intensity  of  respiration  through  its  effect  on  the  other  life  pro- 
cesses.     Respiration    ceases    in    completely   dry   plants    (seeds, 
dry  mosses,   dry  lichens,   certain    spores)   and   is   low    or   alto- 
gether  ceases  in  resting   plants   or   parts   of   plants   as  in  the 
autumn   and  winter.     Oxygen  is  necessary  for  ordinary  respi- 
ration,  and  most  plants  are  of   this  nature.     But  an  increase 
or  decrease  in   oxygen  content  of  the   air  has  little  immediate 
significance. 

189.  Respiration  in  fungi. — While  fungi  cannot  form  sugar, 
or  starch,  they  breathe  like  other  plants.     This  can  be  shown  by 
placing  a  few  half-grown  mushrooms  or  toadstools  in  a  fruit  jar, 
and   closing   it   tightly.     In    10   to  12    hours  the    test  with  the 
barium  hydrate  and  afterwards  with  the  lighted  splinter  shows 
the  presence  of  carbon  dioxide. 

190.  Respiration    necessary   for    growth. — This    can   be 
shown    by    the    following    experiment.     Germinate    some    peas 
until  the  radicles  are  2  to  3  cm.  (about  i  inch)  long.     Have  ready 
a  bottle  with  soaked  peas  as  described  in  paragraph  182  and 
with  a  small  quantity  of  water  in  the  bottom  to  keep  the  air  in 


WORK  OF  LEAVES:   RESPIRATION  113 

the  bottle  moist.  Place  a  piece  of  wet  filter  paper  on  the  peas. 
In  ten  or  twelve  hours  after  some  of  the  oxygen  has  been  used, 
on  this  paper  rest  three  or  four  of  the  germinated  peas.  Close 
the  bottle  tightly.  The  peas  in  the  jar  will  use  up  so  much 
oxygen  and  give  off  so  much  carbon  dioxide  that  ordinary 
respiration  cannot  take  place  in  the  seedling  peas  on  the  filter 
paper.  Fit  up  a  similar  bottle  with  folds  of  wet  paper  and 
some  free  water  in  the  bottom.  Place  a  piece  of  wet  filter  paper 
on  the  folds  of  paper  and  on  this  place  three  or  four  of  the 
seedling  peas  which  have  radicles  of  a  length  equal  to  those  in 
the  other  bottle.  Close  the  bottle  tightly.  In  24  to  48  hours 
compare  the  length  of  the  radicles  of  the  seedlings  in  the  two 
bottles. 

These  experiments  teach  us  that  all  plants,  with  very  few 
exceptions,*  breathe,  or  respire  by  absorbing  oxygen  and  giving 
off  carbon  dioxide. 

191.  Respiration  in  the  absence  of  oxygen. — This  some- 
times occurs.  It  can  be  demonstrated  in  germinating  seeds  by 
placing  them,  when  the  root  is  just  emerging  from  the  seed  coats, 
in  an  inverted  test  tube  filled  with  mercury,  the  lower  end  of 
which  is  immersed  in  mercury  placed  in  another  vessel.  In  the 
course  of  a  day  carbon  dioxide  is  given  off  from  the  seedlings,  and 
being  lighter  than  the  mercury  displaces  some  of  it  and  occupies 
the  upper  part  of  the  inverted  tube. 

The  carbon  dioxide  here  comes  from  the  living  substance  of 
the  peas,  just  as  it  does  in  ordinary  respiration.  There  is  a 
loss  or  waste  of  substance  by  the  peas  which  passes  off  as  car- 
bon dioxide.  This  waste  is  formed  by  a  breaking  down  of 
some  of  the  living  substance  of  the  peas.  The  same  breaking 
down  of  the  living  substance  occurs  in  ordinary  respiration,  but 
oxygen  is  absorbed  from  the  air  to  replace  that  taken  from  the 

*  The  exceptions  are  found  in  some  of  the  low  minute  plants,  for  example, 
some  of  the  bacteria  which  cannot  grow  in  the  presence  of  oxygen.  These 
are  called  anaerobes,  because  they  cannot  carry  on  their  life  processes  in  the 
presence  of  ordinary  air. 


114  GROWTH   AND    WORK   OF   PLANTS 

living  substance,  and  the  carbon  is  replaced  in  the  ordinary*  res- 
piration of  plants  by  the  carbon  which  is  obtained  from  the 
carbon  dioxide  absorbed  in  the  making  of  sugar  and  starch. 

192.  Fermentation  of  yeast. f — Yeast  as  used  in  bread- 
making  to  produce  the  "  rising"  of  the  bread,  causing  it  to 
become  spongy  and  light,  is  composed  largely  of  microscopic 
plants  mixed  in  with  some  food  substances,  etc.  This  micro- 
scopic plant  is  called  the  yeast  plant  or  yeast.  It  is  a  very  inter- 
esting plant,  and  the  work  it  performs  in  bread  "  rising"  is  very 
instructive  in  connection  \vith  this  subject  of  respiration. 

The  tube  and  the  lower  part  of  the  bulb  of  a  fermentation 
tube  is  filled  with  a  solution  of  grape  sugar  or  an  infusion  of 
potato,  $  and  a  small  piece  of  yeast  cake  is  put  in  the  bulb.  This 
is  kept  in  a  warm  place.  As  the  yeast  plant  grows,  bubbles  of 
gas  will  rise  in  the  tube  and  displace  the  solution  which  is  forced 
into  the  bulb.  If  some  pieces  of  caustic  potash  are  placed  in  the 
bulb,  the  potash  solution  absorbs  the  gas  in  the  tube  and  the 
solution  rises  again.  This  shows,  as  we  have  learned  above, 
that  the  gas  is  CO2  which  is  an  index  of  the  respiration  of 
the  yeast  plant,  or  rather  of  the  fermentation  of  the  sugar  in  the 
solution. 

This  fermentation  has  gone  on  largely  in  the  absence  of  air, 
but  it  is  somewhat  at  the  expense  of  growth  and  reproduction  of 
the  yeast  plant,  for  when  air  is  present  growth  and  multiplication 
of  the  yeast  is  more  rapid.  During  the  fermentation  of  the 
sugar  by  the  yeast,  alcohol  is  also  formed.  These  two  products 
of  fermentation  by  the  yeast  plant  are  of  great  importance.  The 
evolution  of  the  gas  carbon  dioxide  in  bread  making  forms 

*  By  ordinary  respiration  is  meant  aerobic  respiration.  Aerobic  respi- 
ration is  carried  on  by  plants  which  require  air.  Anaerobic  respiration  is 
respiration  in  the  absence  of  air.  All  plants  can  carry  on  anaerobic  res- 
piration for  a  short  time,  but  most  plants  are  injured  and  soon  die  or  rest 
if  air  is  not  accessible.  Some  plants  are  active  either  as  anaerobes  or 
aerobes  (the  yeast  plant),  while  others  only  as  anaerobes  (certain  bacteria). 

f  Saccharomyces  cervisese. 

}  If  possible  it  is  well  to  sterilize  the  tube  after  filling  with  the  grape  sugar 
or  infusion.  Also  a  second  tube  for  a  check  is  desirable. 


CHAPTER  XIV. 
SOME  SPECIAL  ASPECTS    OF  NUTRITION   OF  PLANTS. 

SOURCES    OF    PLANT    FOOD. 

197.  The  nutrition  of  plants  includes  a  study  of  the  sources 
of  plant  food,  the  methods  of  absorption  and  transport  of  the 
food  material,  the  chemical  processes  (metabolism)  in  the  elabora- 
tion of  food  materials  in  the  plant,  the  building  up  of  organic 
compounds  used  for  food  and  storage,  and  the  assimilation  of 
material  into  new  plant  substance  and  structures  which  enable 
the  plant  to  grow  and  reproduce  itself.  While  certain  plant  foods 
may  be  derived  under  a  great  variety  of  forms,  there  are  certain 
essential  constituents  of  plant  food  occurring  in  the  various 
compounds.  There  are  two  general  classes  of  plant  food,  the  or- 
ganic compounds  (example,  those  formed  by  plants,  as  carbohy- 
drates, proteids,  etc.)  and  the  inorganic  compounds*  (mineral 
substances,  etc.,  and  those  not  containing  carbon).  The  essential 
food  constituents  or  elements  in  the  organic  compounds  are  carbon, 
hydrogen,  oxygen  and  nitrogen.  In  the  inorganic  compounds  the 
essential  constituents  or  elements  are  calcium,  potassium,  magne- 
sium, phosphorus,  sulphur  and  iron^\  though  calcium  is  not 
essential  to  the  growth  of  the  fungi. 

*  The  terms  organic  compounds  and  inorganic  compounds  are  em- 
ployed here  in  the  older  sense. 

t  There  are  a  number  of  other  elements  which  are  not  essential  constitu- 
ents of  food,  but  are  of  use  to  the  plant.  For  example,  silicon  (flint,  most 
kinds  of  sand,  sandstone,  etc.,  are  oxides  of  silicon)  strengthens  the  stems 
of  the  grains  and  grasses,  and  is  found  in  great  abundance  in  the  stems  of 
the  scouring  rushes  (Equisetum)  which  often  grow  where  there  is  an  abun- 
dance of  sand  in  the  soil.  Many  substances  are  found  in  plants  which  are 
useful  perhaps  in  protecting  the  plants  from  certain  of  their  enemies  by 
rendering  them  distasteful  or  poisonous,  and  many  other  substances  are 
found  which  do  not  appear  to  be  of  any  use. 

117 


Il8  GROWTH   AND    WORK   OF  PLANTS 

198.  Sources  of  plant  food. — The  different  elements,  which 
have  been  found  necessary  constituents  of  plant  food,  are  not 
taken  up  by  the  plant  as  elements,  except  in  rare  cases,  and  possi- 
bly also  with  the  exception  of  the  oxygen  of  respiration.     Oxygen 
is  taken  into  the  plant  as  an  element  in  the  process  of  respiration. 
If  this  oxygen  merely  assisted  in  the  combustion  of  plant  material 
it  would  not  in  this  instance  be  a  food  constituent,  but  there  are 
reasons  for  believing  that  it  is  first  assimilated  into  the  living  matter 
(see  paragraph  185).     Nitrogen  is  taken  up  as  an  element  in  the 
nutrition  of  a  few  specialized  bacteria  (see  fixation  of  nitrogen, 
paragraphs  201-203).     The  mineral  substances  found  in  the  ash 
of  plants  when  they  are  burned,  containing  among  other  things 
calcium,  magnesium,  phosphorus,  sulphur,  iron,  the  plant  takes 
up  from  the  soil  in  the  form  of  nitrates,  sulphates,  phosphates,* 
etc.,  which  are  formed  during  the  weathering  and  disintegration 
of  rocks. |    The  water  (H2O)  of  the  plant  is  absorbed  from  the 
soil.     This  furnishes  part  of  the  hydrogen  and  oxygen.     The 
source  of  the  carbon  for  green  plants  is  the  carbon  dioxide  (CO2) 
of  the  air,  which  the  plant  uses  during  photosynthesis.     Nitrogen 
is  obtained  by  absorption  of  nitrates  from  the  soil  and  from  some 
other  compounds  of  nitrogen.     For  example,   in  cultivated  or 
waste  fields,  the  nitrogen  food  is  mostly  in  the  form  of  nitrates, 
while  nitrates  are  scarce  in  the  forest  where  there  is  an  abundance 
of  decaying  leaves  and  humus.     In  the  forest  the  nitrogen  food 
is  chiefly  in  the  form  of  ammonia  compounds  (NH3). 

199.  Most  of  the   substances  used  as  plant  food  from 
the  soil  exist  there  in  quantities  sufficient  to  last  plants 
for  many  years. — But  nitrogen  compounds  are  rare,J  and  if 

*  Examples,  potassium  nitrate,  calcium  sulphate,  magnesium  sulphate, 
calcium  phosphate,  etc. 

f  The  small  particles  of  rock  make  the  basis  of  the  soil,  while  dead  plant 
remains  furnish  the  organic  matter  and  humus  which  give  it  a  darker  color 
and  make  it  more  retentive  of  moisture. 

J  Phosphates  are  also  comparatively  rare  in  many  soils,  and  during 
continued  cropping  when  they  are  not  returned  to  the  soil,  the  soils  become 
deficient.  Phosphorus  occurs  in  the  oldest  rocks  and  these  phosphates 
appear  in  the  soil  from  disintegration  of  rock.  By  the  growth  of  plants  they 


SPECIAL  ASPECTS  OF  NUTRITION  OF  PLANTS      119 

abundant  in  some  soils  are  usually  soon  exhausted  or  reduced  to 
such  a  small  quantity  that  the  plants  indicate  the  deficiency  of 
the  soil  in  nitrogen,  by  their  poor  and  often  sickly  growth. 
Uncultivated  soils,  where  the  plant  covering  is  left  to  decay,  grad- 
ually become  richer  in  plant  foods.  Cultivation  of  crops  tends 
to  impoverish  the  soil,  if  the  plant  foods  taken  out  are  not  re- 
plenished, since  mineral  substances  and  nitrogen  are  removed  in 
the  harvesting  of  the  crop.  The  most  costly  plant  food  is  nitrogen, 
or  nitrogenous  fertilizers.  Stable  manure  is  rich  in  nitrogen 
(ammonia  compounds)  and  is  also  beneficial  to  soil,  since  the 
plant  remains  in  it  improve  the  physical  condition  of  the  soil 
(see  nitrification,  paragraph  200).  Among  commercial  ferti- 
lizers nitrogen  is  obtained  in  cotton  seed  meal;  guano,  the  excre- 
ment of  birds  found  in  rich  deposits  on  certain  islands  near 
southern  sea  coasts;  Chili  saltpeter,  a  nitrate  of  soda  found  in 
great  deposits  in  Chili  and  Peru,  etc.  These  latter  supplies  of 
nitrogen  are  becoming  exhausted.  Indeed  were  it  not  for  the 
fact  that  certain  processes  in  nature  are  going  on  by  which 
nitrogen,  a  gas  constituting  four-fifths  of  the  air,  is  fixed,  i.e., 
combined  into  nitrogenous  substances,  and  made  available  for 
plant  food,  the  supplies  of  nitrogenous  food  would  become 
exhausted,  since  in  the  process'  of  decay  (especially  in  the 
absence  of  air)  and  by  fire,  the  nitrogen  fixed  in  compounds  is 
set  free  as  a  gas. 

NITRIFICATION. 

200.  Nitrification. — It  has  been  pointed  out  above  that  in 
the  fields  the  combined  nitrogen  absorbed  by  plants  is  usually  in 
the  form  of  nitrates,  while  in  the  forest  where  there  is  much 

are  removed  from  the  soil  and  concentrated.  They  are  farther  concen- 
trated by  animals  which  feed  on  plants,  as  well  as  by  carnivorous  animals. 
On  the  death  of  the  animals  they  are  again  returned  to  the  soil,  and  often  are 
deposited  in  considerable  quantities  in  rocks  forming  extensive  deposits 
known  as  phosphate  rock.  Large  beds  of  this  phosphate  rock  are  very 
valuable,  and  the  rock  is  quarried,  ground  and  sold  as  a  fertilizer  for  the  soil. 
Extensive  beds  which  have  been  of  great  commercial  value  exist  in  Eastern 
South  Carolina,  but  are  now  nearly  exhausted.  Other  beds  of  phosphate 
rock  exist  in  Florida  and  recently  some  have  been  discovered  in  the  West. 


120  GROWTH  AND    WORK   OF  PLANTS 

humus  it  is  usually  in  the  form  of  ammonia  (NH3).  In  the  fields 
the  ammonia  would  soon  volatilize  and  pass  off  in  the  gaseous 
form  in  the  air  and  be  lost.  Ammonia  is  often  applied  to  the 
soil  in  fertilizing  (in  stable  manure).  "Ammonia  is  also  formed  in 
the  decay  of  plant  parts  and  animals  (especially  in  the  absence  of 
air  which  is  the  case  in  bulky  parts,  and  in  soil).  The  proteid 
substances  are  split  into  ammonia  by  the  ferment  action  of  cer- 
tain bacteria.  This  process  is  called  denitrification,  and  is  the 
opposite  of  nitrification.  The  denitrifying  bacteria  can  only  act 
on  the  protein  substances  and  nitrates  in  the  absence  of  oxygen. 
They  obtain  oxygen  from  that  combined  in  the  nitrogenous  sub- 
stance which  they  denitrify.  This  is  another  example  of  anaero- 
bic respiration.  (See  paragraph  191.)  For  the  conservation  of 
this  ammonia  it  is  very  important  that,  as  it  is  formed,  it  shall  be 
converted  into  a  more  stable  form  which  will  not  volatilize,  and 
which  will  still  be  available  as  plant  food,  for  while  it  has  been 
shown  that  corn  and  a  number  of  other  plants  can  thrive  as  well 
when  fed  on  ammonia  compounds  as  when  fed  on  nitrates,  in 
practice  a  large  part  of  the  ammonia  would  be  lost  if  it  were  not 
immediately  changed  to  nitrates  (i.e.,  nitrified).  The  process  by 
which  ammonia  is  nitrified  is  termed  nitrification,  and  it  is  one  of 
the  most  important  processes  in  nature  for  the  nutrition  of  plants. 
Nitrification  is  brought  about  by  two  different  kinds  of  very 
minute  bacteria,  called  nitrite  bacteria  (Nitromonas)  and  nitrate 
bacteria  (Nitrobacter).  These  bacteria  are  widely  distributed  in 
the  soil  over  the  earth  (though  not  so  plentiful  in  the  forest). 
The  nitrite  bacteria  convert  the  ammonia  into  nitrous  acid,  and 
then  the  nitrate  bacteria  convert  this,  into  nitric  acid  which  unites 
with  another  substance  *  and  forms  nitrates.  This  process  supplies 
them  with  energy  so  that  they  are  able  to  assimilate  free  oxygen 
from  the  air. 

FIXATION    OF    NITROGEN. 

201.    If  the  free  nitrogen  of  the  air  were  available  as  such  for 
food  by  all  plants,  one  of  the  serious  problems  of  the  agriculturist 
would  be  satisfactorily  solved,  and  many  plant  and  animal  foods 
*  This  substance  is  called  by  chemists  a  base. 


SPECIAL  ASPECTS  OF  NUTRITION  OF  PLANTS      121 

for  man  would  be  greatly  reduced  in  price.  In  former  years  it 
was  held  by  some  scientific  men,  that  -the  ordinary  green  plants 
could  use  directly  the  free  nitrogen  of  the  air  for  food.  Careful 
experiments  have  demonstrated,  however,  that  this  is  not  the 
case.  Still  it  has  been  known  for  many  years,  that  leguminous 
plants  (clover,  peas,  beans,  alfalfa,  vetches,  honey  locust,  soja 
beans,  etc.)  will  grow,.. thrive,  anjl  bear  a  good  crop  in  soil  very 
poor  in  m'trop^nous  plant  food  provided  the  other  conditions  are 
favorable. 

202.  Root   tubercle   bacteria. — Careful   investigations  have 
shown  that  this  is  due  to  the  work  of  microorganisms*  in  the 
roots  of  these  plants.     These  bacteria  are 

widely  distributed  over  the  earth  in  nearly 
all  soils,  especially  in  regions  where  legum- 
inous plants  grow.      These  bacteria  enter 
at  the  root  hairs,  extend  by  growth  in  the 
form  of  a  thread  into  the  cortical  region  of 
the  root  where  they  stimulate  the  root  cells 
to  the   formation  of    a   gall   or   tubercle, 
which  is  often  of  different  form  in  different 
species  of  legumes.     These  root  tubercles 
are  short  and  thick,  often  oval  in  form,  or 
short,  cylindrical  and  branched.    They  are 
stouter  than  the  roots  to  which  they  are     Root  of  ^common  vetch, 
attached,  so  that  they  are  easily  seen  when  showing  root  tuber 
the  clover,  pea  or  other  legume  is  dug  up  and  the  soil  carefully 
washed  from  the  roots  (fig.  90). 

203.  Within  the  root   tubercle   the   bacteria   spread   by 
means  of  branched  threads  or  tubes.     The  cells  of  the  tubercle 
are  rich  in  protoplasm.     Within  the  cells  great  numbers  of  free 
bacteria  are  formed  which  are  oval  or  rod-like  or  Y  or  X  shaped. 
The  bacteria  in  this  condition  are  filled  with  nitrogenous  sub- 
stances which  they  have  formed  by  assimilating  (or  ''fixing") 

*  Certain  bacteria,  also  called  microbes.  The  name  now  generally  used 
for  this  particular  microorganism  is  Pseudomonas  radicicola.  Earlier  names 
are  Phytomyxa  legutninosarum,  Rhizobium  leguminosarum,  etc. 


122  GROWTH  AND    WORK  OF  PLANTS 

free  nitrogen  which  they  have  absorbed  from  the  air  in  the  soil, 
with  carbohydrates  and  other  organic  substances  which  they 
have  absorbed  from  the  cells  of  the  clover  or  other  legume.  The 
bacteria  thus  obtain  their  carbohydrate  food  from  their  "  host," 
and  to  this  extent  they  have  lived  as  parasites  at  its  expense. 
But  they  do  very  little  if  any  injury  to  the  clover.  In  fact  many 


Fig.  91.  Fig.  92. 

Root  tubercle  organism  from  vetch,  old  Root  tubercle  organism  from  Medicago 

condition.  denticulata. 


of  these  bacteria  charged  with  this  "  fixed"  nitrogen  die  within 
the  root  tubercle,  and  the  clover  or  pea,  or  other  host  as  the  case 
may  be,  is  able  to  absorb  this  nitrogenous  substance  and  appro- 
priate it  to  its  own  use.  This  is  why  leguminous  plants  thrive 
so  well  in  soils  poor^in  nitrogenous  pjant  food.  After  a  time  stm* 
of  the  root  tubercles  die  and  some  of  the  nitrogen  "  fat"  bacteria 
(often  called  bacteroids)  are  set  free  in  the  soil  and  thus  enrich 
the  soil.  Some  of  the  living  bacteria  are  also  set  free  in  the  soil 
so  that  the  soil  contains  numbers  of  them  to  attack  succeeding 
legume  crops.  Even  when  the  crop  of  clover,  or  peas,  etc.,  is 
removed  from  the  ground  the  soil  becomes  richer  in  nitrogenous 
substance  because  of  the  bacteroids  left  in  the  root  tubercles. 
But  more  nitrogenous  plant  food  is  added  to  the  soil  in  the  pro- 
cess of  "  green  soiling"  such  crops,  i.e.,  in  plowing  the  clover  or 
peas  under  (see  also  Mycorhiza,  and  Symbiosis,  paragraphs  205, 
206). 

204.   Inoculation  of  soil  with  the  root  tubercle  bacteria. — 
If  some  of  the  soil,  where  clover  or  peas  have  grown  with  these 


SPECIAL  ASPECTS  OF  NUTRITION  OF  PLANTS       12$ 

bacteria  in  their  roots,  be  spread  on  soil  poor  in  combined  nitrogen 
where  these  or  related  crops  have  not  been  grown  recently,  the 
clover  or  peas  will  develop  a  greater  number  of  root  tubercles  and 
consequently  more  nitrogen  will  be  fixed  to  the  benefit  of  the  crop 
and  to  the  enrichment  of  the  soil  in  combined  nitrogen.  This 
inoculation  of  the  soil  has  been  put  into  practice  in  a  number  of 
different  ways.  One  of  the  more  recent  methods  is  by  preparing 
in  the  laboratory  "  pure  "  cultures  of  the  bacteria  on  nitrogen- 
poor  culture  media  in  small  tubes  which  can  be  sold  and  sent  by 
mail  to  persons  who  wish  to  inoculate  their  soils.*  The  object  in 
growing  them  on  nitrogen-poor  substances  is  to  create  in  them 
"  nitrogen  hunger,"  for  they  will  then  more  readily  attack  the 
roots  of  the  clover,  etc.,  in  order  to  put  them  in  a  condition  to 
"  fix  "  the  free  nitrogen.  In  soil  rich  in  combined  nitrogen  they 
do  not  readily  attack  the  roots  of  the  legumes.  It  is,  therefore, 
not  good  policy  to  inoculate  soils  rich  in  combined  nitrogen,  for 
the  clover,  etc.,  will  find  a  sufficient  amount  in  the  soil  already. 
There  have  been  some  successes  and  many  failures  in  inoculating 
soils  with  the  root  tubercle  bacteria.  Some  of  the  failures  are  to 
be  ascribed  to  a  poor  condition  of  the  inoculating  material.  Other 
failures  are  probably  due  to  the  fact  that  the  soil  is  already  rich  in 
combined  nitrogen,  and  still  others  are  probably  due  to  the  fact 
that  there  are  a  sufficient  number  of  organisms  already  in  the 
soil.  Some  of  the  conditions  under  which  one  might  hope  for 
good  results  are,  first,  when  the  soil  is  poor  in  combined 
nitrogen  and  Ihere  are  few  root  tubercle  bacteria  already  in 
the  soil;  second,  when  the  soil  is  poor  in  combined  nitrogen 
and  the  root  tubercle  bacteria  may  be  plentiful,  but  of  a 
"  race  "  different  from  that  which  readily  attacks  the  kind  of 
legume  it  is  desired  to  grow.  For  example,  the  race  of  bacteria 
which  attack  the  roots  of  clover  will  not  readily  attack  the  roots 
of  the  soja  bean.  Those  which  attack  peas  will  not  readily 
attack  the  locust,  etc. 

*  See  Bull.  No.  71  Bureau  PI.  Ind.  U.  S.  Dept.  Agr.,  Soil  Inoculation  for 
Legumes  :  Bull.  No.  72,  Pt.  IV,  Inoculation  of  Soil  with  Nitrogen-Fixing 
Bacteria. 


124  GROWTH   AND    WORK   OF  PLANTS 

MYCORHIZA,  SYMBIOSIS. 

205.  Mycorhiza. — The  intimate  union  of  bacteria  or  fungi 
with  the  roots  of  plants,  similar  to  that  described  in  the  preceding 
paragraphs,  gives  rise  to  an  interesting  and  complex  structure 
the  work  of  which  is  different  from  that  of  either  part  of  this  struc- 
ture alone.  Such  a  structure  is  called  a  mycorhiza*  There  are 
many  kinds  of  mycorhizae,  but  they  all  may  be  arranged  into  two 
general  kinds.  Those  where  the  fungus  part  is  inside  of  the  root 
are  endotrophic  mycorhiza,  while  those  in  which  the  fungus  part 
surrounds  the  root  are  called  ectotrophic  mycorhiza.  The  root 
tubercles  are  endotrophic  mycorhizae.  An  example  of  an  ecto- 
trophic mycorhiza  is  found  in  trees  of 
the  oak  family  (oak,  beech,  hornbean, 
etc.)  and  some  other  trees  where  the 
tips  of  the  roots  are  covered  with  a 
dense  felt  of  fungus  threads  (fig.  93). 
This  occurs  in  the  forest  where  there 
is  abundant  humus  (the  decaying  leaf 
mold),  but  is  not  always  present  in 
the  same  species  of  trees  when  growing 
in  fields  where  humus  is  absent.  The 
dense  mat  of  fungus  threads  on  the 

Beech  root  grown  in  unsterilized     outside     of    the    young    TOOtS    prevents 
wood   humus  ;    p,  strands  of  fungal 

hypha;,  at  a  associated  with  humus,   the    development   of   root   hairs,    and 

Magnified    several    times.      (After  . 

Frank.)  some  of  the  threads  penetrate  into  the 

cells  of  the  roots.  The  trees,  under  these  circumstances,  are 
dependent  on  the  threads  of  the  fungus  for  the  absorption  of  water 
and  food  solutions  from  the  soil,  the  threads  thus  acting  as  root 
hairs.  There  are  great  advantages  to  the  forest  trees  in  this  as- 
sociation with  the  fungus  mycelium.  The  fine  fungus  threads, 
extending  from  the  mycorhiza,  branch  and  reach  out  in  all  direc- 
tions, penetrating  the  humus  better  than  root  hairs  could.  They 
have  the  power  of  decomposing  certain  insoluble  nitrogen  com- 
pounds and  of  passing  them  over  to  the  tree.  They  also  can 
change  the  ammonia  compounds,  so  abundant  in  humus,  into  an 
*  From  fj-faijs  =  mold,  and  ^ifa  =  root. 


SPECIAL  ASPECTS  OF  NUTRITION  OF  PLANTS       12$ 

available  form  for  the  forest  trees.  It  is  supposed  that  the  fungus 
mycelium  obtains  some  benefit  from  this  association  with  the  roots 
of  trees,  but  this  is  not  well  understood.  These  mycorhizae  are 
shorter,  stouter  and  also  branched  more  than  the 
normal  roots.  This  difference  in  form,  as  well  as 
their  more  complex  structure,  renders  the  name 
mycorhiza  appropriate  and  useful.  In  some  cases 
these  fungus  threads  are  the  spawn  of  certain 
mushrooms  and  puff  balls.  The  mycelium  of  the 
truffle,  an  edible  fungus  of  great  commercial  value 
in  southern  France  and  in  Italy,  is  supposed  to  have 
a  similar  relation  to  the  roots  of  certain  forest  trees. 
206.  Symbiosis. — This  living  together  in  close 
physiological  relation  of  two  different  organisms  is 
called  symbiosis.  In  the  case  of  the  root  tubercles  Fi«-  M. 

,  .  .  i  i      •         •  r  Beech  root  in  wood 

or  leguminous  plants  the  relation  is  one  or  mutual  humus  freed  from 

....        .  fungus,  root  hairs  h. 

benefit,  each  partner  in  the  symbiosis  (each  partner  (After  Frank.) 
is  a  symbiont)  deriving  some  benefit  from  the  other.  The  same  rela- 
tion is  supposed  to  exist  in  the  case  of  the  mycorhiza  of  forest  trees. 
This  kind  of  symbiosis  is  called  mutiialistic  symbiosis.  Another 
well-known  example  is  seen  in  the  case  of  the  lichens  (see  paragraph 
432).  Another  kind  of  symbiosis  occurs  in  the  relation  of  a  parasite 
to  its  host  where  the  parasite  living  on  or  in  the  host  injures  or  kills  it 
but  the  host  receives  no  benefit.  This  is  antagonistic  symbiosis.  So 
there  is  contact  symbiosis  where  two  organisms  living  side  by  side, 
work  together,  each  one  supplying  the  other  with  some  product  of  its 
work.  An  example  of  this  is  seen  in  the  case  of  the  bacterium  (Clos- 
tridium  pasteurianum)  which  lives  in  the  soil  in  conjunction  with 
two  green  algae.  The  algae  supply  the  bacterium  with  carbohydrates 
and  it  is  then  able  to  fix  free  nitrogen  and  this  combined  nitrogen  can 
be  used  by  the  algae.  Related  to  this  but  a  step  farther  are  the  many 
cases  of  metabiosis  where  successive  organisms  digest  or  ferment 
the  product  of  previous  ones.  Example,  a  common  mold  (Asper- 
gilliis  oryzcz]  growing  on  rice  converts  the  starch  into  sugar,  then 
yeasts  ferment  the  sugar  to  alcohol,  and  then  the  acetic  acid 
bacteria  ferment  the  alcohol  to  acetic  acid. 


CHAPTER   XV. 


NUTRITION  OF    PARASITES   AND    SAPROPHYTES. 

207.  A  parasite  is  an  organism,  plant  or  animal,  which 
lives  on  or  in  another  living  organism  at  its  expense,  deriving  all 

or  a  part  of  its  nourishment  from  it. 
The  plant  or  animal  on  which  the  parasite 
lives  is  called  the  "  host."  The  parasite 
derives  a  part  or  all  of  its  food  from  its 
host,  usually  inflicting  more  or  less  injury 
upon  the  host  or  even  causing  its  death. 
Parasitic  plants  are  represented  in  nearly 
all  the  great  branches  of  the  plant  king- 
dom. There  are  some  among  the  flower- 
ing plants,  some  among  the  algae,  the  fungi 
and  bacteria,  but  by  far  the  greater  num- 
ber are  found  among  the  fungi  and  bac- 
teria. One  reason  for  this  is  that  none 
of  the  fungi  or  true  bacteria  have  chloro- 
phyll; therefore,  they  cannot  fix  carbon, 
that  is,  cannot  make  their  own  carbo- 
hydrate foods,  but  are  dependent  on 
chlorophyll-bearing  plants  for  it.  The 
fungi  and  bacteria  which  are  parasitic  on 
green  plants  then  obtain  their  carbohy- 
drates directly  from  their  hosts.  Those 
which  are  parasitic  on  animals  derive 
their  carbon  food  from  animals,  but 
animals  get  their  carbohydrates  directly  from  green  plants,  which 
they  eat,  or  in  the  final  analysis  from  plants  or  animals  which  do 
feed  on  green  plants  either  dead  or  alive. 

208.  The   fungi   and   bacteria  which   are   not   parasites 
derive  their  carbohydrate  food  by  growing  on  dead  plants  or 

126 


Fig.  95. 

A  saprophytic  tungus  (Cre- 
pidotus)  growing  on  a  rotten 
limb  in  the  iorest. 


NUTRITION  OF  PARASITES  AND  SAPROPHYTES      I2/ 


animals  or  on  their  remains,  that  is,  on  organic  matter.  Such 
plants  are  called  saprophytes,  a  plant  having  the  life  relation  of 
nutrition  to  dead  or  decaying  organisms.  The  largest  number  of 
species  of  both  bacteria  and  fungi  are  saprophytes,  and  many  of 
them  do  very  important  work  in  the  economy  of  nature,  reducing 
the  substance  of  dead  plants  to  the  condition  of  humus  which 
improves  the  mechanical  condition  of  the  soil,  removes  the  bulky 
parts  of  plants,  and  sets  free  many  substances  which  can  be  used 
again  for  food  by  the  green  plants.  Examples  of  these  fungi  are 
the  mushrooms,  toadstools,  puff  balls,  bracket  fungi,  molds,  etc. 

NUTRITION    OF    PARASITES. 

Although  the  larger  number  of  parasites 
are  among  the  fungi  and  bacteria  there 
are  many  parasitic  flowering  plants.  A  few 
of  these  are  briefly  described  here. 

209.  Nutrition  of  the  dodder.— The 
dodder,  or  "  love  vine"  (Cuscuta),  is  a 
slender  twining  plant  which  is  parasitic 
on  clover,  or  some  other  cultivated  plants 
and  on  a  great  many  weeds.  There  are 
several  species.  The  plant  has  very  in- 
conspicuous flowers  developed  in  crowded 
clusters.  The  seeds  are  small.  When 
the  seeds  germinate  on  the  ground  a  root 
is  formed  which  attaches  the  plant  to  the 
soil.  But  when  the  slender  vine  twines 
around  the  living  stem  of  its  host,  at  the 
places  of  contact  it  develops  wedge-shaped 
outgrowths  which  pierce  the  stem  of  the 
host  and  penetrate  the  nbro-vascular 
bundles.  These  outgrowths  are  haustoria, 
or  suckers,  because  they  attach  the  vine 
to  its  host  and  serve  as  absorbent  organs. 
There  are  nbro-vascular  bundles  in  the 
haustoria  which  connect  with  those  of  the  vine  and  also  form  an 


Fig.  96. 

Dodder,  showing  stems 
twining  around  its  host  (Im- 
patiens). 


128  GROWTH   AND    WORK   OF  PLANTS 

intimate  connection  with  those  of  the  host.  Through  these 
haustoria  the  dodder  absorbs  solutions  of  mineral  substances, 
and  also  of  carbohydrates  and  proteids  manufactured  by  its 
host.  Receiving  these  food  substances  already  prepared  the 
parasite  has  no  need  of  chlorophyll  nor  of  expanded  leaves.  In 
accordance  with  the  general  law,  therefore,  that  when  an  organ 
ceases  to  function  it  becomes  reduced  or  discarded,  the  leaves  of 
the  dodder  have  become  reduced  to  mere  scales  on  the  stem,  and 
the  root  dies  as  soon  as  the  vine  becomes  attached  to  its  host  by 
the  haustoria.  The  vine  and  its  scale  leaves  are  pale  yellowish  in 
color.  The  seeds  of  the  dodder  germinate  in  the  soil  developing 
a  true  root  and  a  slender  vine  which  lives  an  independent  exist- 
ence at  the  expense  of  the  food  stored  in  the  seed.  The  slender 
vine  extends  out  and  around  until  it  comes  in  contact  with 
some  plant  part,  when  it  develops  the  haustoria  (or  "sinkers" 
as  they  sometimes  are  called)  and  then  the  root  in  the  soil 
dies. 

210.  Nutrition  of  the  mistletoe  (Phoradendron  flavescens). 
—The  mistletoe  is  a  well-known  plant  especially  in  the  southern 

half  of  the  United  States,  and  is  often  used  farther  north  in 
Christmas  decorations.  It  is  a  parasite  on  a  number  of  trees, 
especially  on  red  maple  and  the  tupelo,  but  occurs  on  the  oaks 
and  some  other  trees.  It  is  a  small  branched  shrub  often  forming 
dense  tufts  on  the  branches  of  its  host.  It  is  very  conspicuous  in 
winter  because  it  holds  its  leaves  while  its  hosts  are  bare,  and 
because  of  its  green  stems.  Having  chlorophyll  it  can  manu- 
facture its  own  carbohydrates.  Its  roots  penetrate  the  branches 
of  the  trees  on  which  it  grows,  and  it  derives  its  mineral  foods 
and  water  from  its  host. 

211.  Other  parasitic  flowering  plants  are  the  beech  drops 
(Epiphegus)  growing  attached  to  the  roots  of   beech  trees,  the 
small  mistletoe  (Arceuthobium)  attached  to  twigs  and  branches  of 
the  native  spruce.    The  mistletoe  of  Europe  (Viscum  album)  grows 
on  a  great  variety  of  trees,  but  develops  more  freely  and  luxu- 
riantly on  apple  trees,  the  black  poplar  and  certain  spruces,  trees 
which  have  a  soft  cortex,  while  it  is  rarer  on  the  beech,  birch, 


NUTRITION  OF  PARASITES  AND  SAPROPHYTES       I  2Q 


etc.     It  becomes  a  great  pest  sometimes  in  apple  orchards,  and 

the  farmers  are  said  to  welcome  the  collectors  who  gather  it  for 

Christmas  "  greens." 

212.  Nutrition  of  para- 
sitic   fungi.  —  Examples 

of   the    parasitic    fungi    are 

the  rusts  of  grains,  grasses 

and     many     other     plants; 

the    smut   of    corn,  cereals, 

etc.,   the   powdery   mildews, 

the     downy     mildews,    etc. 

(See   Chapters  XXVII   and 

XXVIII.)     Here   it  is  only 

necessary  to   describe    their 

mode  of  nutrition.     In  the 

growing    stage    these    fungi 

produce    slender     branched 

thread-like  structures  which 

spread  in  the  form  of  a  mold 

over    the    surfaces    of    the 

leaves,  or  penetrate  into  the 

tissues  of  their  hosts.     The  absorption  of  food  substance  takes 

place  either  directly  by  the  threads 
of  the  fungus,  or  the  threads  de- 
velop specialized  short  branches, 
simple  or  branched,  which  penetrate 
the  cell  walls  and  lie  in  the  proto- 
plasm of  the  host  cell.  These 
special  branches  are  the  haustoria. 
They  absorb  food  substances  which 

Cells  from  tl/sfenfof  a  rusted  carna-    flow    to    the    threads  of    mycelium* 
tion,  showing  the  intercellular   mycelium    _..i-  fuAV   enrmlv  material    fnr   it* 

and  haustoria.  object  magnified  3o  times  where  they  supply  material  ror  its 

continued  growth  and  later  for  the 

development  of  the  reproductive  bodies.    Some  of  these  fungus 

parasites  often  deform  their  host,  stimulating  the  tissues  to  the 

*  Mycelium  is  the  special  name  of  the  fungus  threads. 


Fig.  97- 

Rust  of  carnation  stems  and  leaves  caused  by  a 
parasitic  fungus  (Uromyces  caryophyllinus). 


I3O  GROWTH   AND    WORK   OF  PLANTS 

formation  of  excrescences  or  galls,  as  in  corn  smut,  the  cedar 
apples,  azalea  apples,  black  knot  of  the  plum  and  cherry,  leaf 
curl  of  peach,  plum  pockets  of  the  plum,  etc. 


NUTRITION    OF    SAPROPHYTES. 

313.  Humus  saprophytes. — Humus  is  composed  of  organic 
matter,  largely  plant  remains  in  a  state  of  decay.  It  is  abundant 
on  the  forest  floor  and  in  moors  where  the  decomposition  of  the 
plant  remains  is  slow  and  incomplete.  As  stated  in  the  opening 
paragraph  of  this  chapter,  saprophytes  are  plants  which  grow  and 
feed  on  dead  or  decaying  organic  matter.  Humus  saprophytes 
are  those  plants  which  grow  in  and  feed  on  humus.  The  humus 
is  not  easily  soluble,  and  is  rendered  available  as  food  for  the  higher 
plants  by  the  solvent  action  of  fungi  and  bacteria.  Many  fungi, 
especially  the  mushrooms,  toadstools,  puff  balls,  etc.,  are  humus 
saprophytes.  Many  species  grow  in  the  forest.  The  threads  of 
mycelium  permeate  through  the  humus  carrying  on  the  disinte- 
gration which  was  begun  by  other  species  and  by  bacteria,  and 
appropriating  for  food  some  of  the  dissolved  substances.  It  is  by 
this  means  that  the  fungus  part  of  the  mycorhiza  (see  paragraph 
205)  prepares  food  for  the  forest  trees  with  which  it  is  associated. 
Some  of  the  flowering  plants  which  grow  in  humus  lack  chloro- 
phyll, and  some  or  all  of  their  roots  are  mycorhizae.  These  are 
also  regarded  as  humus  saprophytes.  The  Indian  pipe  (Mono- 
tropa)  is  one  of  these.  This  is  a  pretty  little  plant  usually  growing 
in  a  cluster  15  to  20  cm.  (6-8  inches)  high.  It  is  white  in  color, 
sometimes  with  a  reddish  tinge.  The  stems  are  straight  and 
fleshy,  the  leaves  are  scale-like  and  lack  chlorophyll.  The  flower 
in  one  common  species  (M.  uniflora)  is  single,  and  is  turned  on 
the  stem  like  the  bowl  of  a  pipe.  This  plant  obtains  its  food 
through  the  mycorhiza.  This  mycelium  has  the  power  of  dis- 
solving some  of  the  carbohydrates  in  the  humus  and  passing  it 
over  to  the  mycorhiza  so  that  the  plant  can  be  supplied  in  this  way 
with  the  carbohydrate  food  which  it  cannot  make  from  the  carbon 
dioxide  of  the  air  because  of  the  absence  of  chlorophyll. 


NUTRITION  OF  PARASITES  AND  SAPROPHYTES      131 


214.  Saprophytic  fungi. — The  humus  saprophytes  mentioned 
in  the  preceding  paragraph  are  of  course  saprophytic  fungi,  and 
the  term  saprophytic  fungi  applies  not  only  to  these  humus  sapro- 
phytes but  to  all  fungi  which  grow  on  dead  and  decaying  organic 
matter.     But  there  are  many  saprophytic  fungi  which  grow  on 
plant  remains  which  are  not  in  the  condition  to  which  we  apply 
the  term  humus. 

215.  The  wood  destroying  fungi  which  are  so  common  on 
dead  logs,  stumps,  branches  and  even  some  species  on  the  living 
trees    are    also    saprophytic    fungi. 

Many    of    those    which    grow    on 

living  trees  are  not  parasites  since 

they  cannot  attack  a  sound   tree. 

They  can  only  enter  the  tree  when 

it    has    been   injured    so    that   the 

living  cambium  layer  (see  paragraph 

100)  is  destroyed  at  a  given  point 

or   has  been  broken  through,  i.e., 

at  wounds  in  the  tree.    The  wounds 

are  produced  in  a  variety  of  ways; 

by  wind,  heavy  snows,  the  felling 

of  timber,  etc.,  branches  are  broken 

off,    or    the    cambium    is    broken 

through;  or  by  fire  which  kills   the 

cambium.     The  heart  wood  which 

is  therefore  sound,  but  dead,  is  thus 

exposed.      The  germs  (spores,    see 

Chapter    XXIX)    carried    by    the 

wind,  lodge  on  these  wounds,  germinate  and  form  the  fungus 

threads  which  grow  into  the  heart  wood  and  thus  gain  access  to 

the  heart  of  the  tree  trunk.     The  threads  of  mycelium  are  enabled 

to  perforate  the  cell  walls  by  the  excretion  of  a  ferment  or  enzyme 

(cytase)  which  dissolves  an  opening  in  the  wall.     Here  they  cause 

"  heart  rot  "  of  the  tree  and  render  the  tree  unfit  for  timber.     The 

fungus  lives  here  for  years,  and  now  and  then  during  certain 

seasons  the  mycelium  develops  to  the  outside  through  the  wounds 


Fig.  99- 

A  wound  parasite  (Polyporus  bore- 
alis)  causing  heart  rot  of  the  hemlock 
spruce.  The  fruit  bodies  are  shelving, 
white  and  overlap  each  other.  The 
mycelium  extends  through  the  heart 
wood  to  the  topmost  branches  and  out 
into  the  roots. 


132 


GROWTH   AND    WORK  OF  PLANTS 


Fig.  100. 

Spawn  of  the  polyporus  as  it  makes  its  way 
through  the  wood  of  the  tree. 


and  forms  the  well-known  bracket  fungi  so  common  in  the  forests, 
or  in  the  case  of  other  species  forms  the  toadstools  or  mushrooms 
often  seen  growing  from  the  wounds  of  trees.  Some  of  these  same 

wood-destroying  fungi  grow 
on  the  dead  logs,  stumps  and 
branches  forming  the  brackets 
or  mushrooms  which  are  the 
fruiting  bodies.  The  myce- 
lium disintegrates  the  cellulose 
and  wood.*  After  these  have 
finished  their  work,  other  spe- 
cies come  in  and  carry  the 
disintegration  farther,  and  so 
on  until  the  wood  is  reduced 
to  humus  when  still  other 
species  grow  on  this.  The 
dead  leaves  are  attacked  by 
still  other  species  and  by  a  similar  series  of  fungus  forms  are 
reduced  to  humus. 

216.  The  molds  which  are  also  fungi,  are,  many  of  them, 
saprophytic  also.     They  grow  on  fruits,  preserves,  old  bread  and 
isolated  plant  parts  which  are  not  humus  (see  the  bread  mold  in 
Chapter  XXVI). 

217.  Decay. — All  decay  is  due  to  the  action  of  living  organisms, 
chiefly  fungi  and  bacteria.     If  these  organisms  could  be  excluded 
from  fruits,  vegetables,  preserves,  meats,  or  any  plant  or  animal 
part,  these  organic  substances  would  be  preserved  indefinitely 
and  if  exposed  to  the  air  would  simply  dry  out.     Dried  beef  is 
rendered  safe  from  decay  because  the  percentage  of  moisture  is 
insufficient  for  the  growth  of  bacteria.     Fruits  which  are  first 
heated  to  kill  the  germs  of  fungi  and  bacteria  and  then  sealed  in 
"  cans  "  to  shut  out  the  air  and  the  entrance  of  germs,  are  pre- 

*  The  mycelium  of  some  of  the  bracket  fungi  (Polyporus  mollis,  for  ex- 
ample) dissolves  only  the  cellulose  of  the  wood  leaving  the  xylogen,  while 
others  (Trametes  pini,  for  example)  dissolve  only  the  xylogen,  leaving  the 
pure  cellulose  intact  in  which  the  xylogen  was  infiltrated. 


NUTRITION  OF  PARASITES  AND  SAPROPHYTES      133 

served.  In  some  very  dry  climates,  trees  when  they  fall  are 
preserved  in  a  sound  condition  for  a  long  time  because  the  mois- 
ture is  insufficient  to  favor  a  rapid  growth  of  the  mycelium  of  the 
wood-destroying  fungi.  The  processes  of  disintegration  of  wood 
and  leaves  described  in  paragraph  215  are  processes  of  decay. 
If  it  were  not  for  such  organisms  as  the  fungi  and  bacteria,  our 
forests  would  soon  become  choked  up  with  dead  trees,  and  nitrog- 
enous foods  in  the  soil  would  in  time  become  used  up  so  that  all 
life  would  disappear  from  the  earth.  The  fungi  are  chiefly  con- 
cerned in  the  disintegration  and  decay  of  carbohydrates,  as  starch, 
sugar,  cellulose  and  woody  structures,  while  bacteria  are  chiefly 
concerned  in  the  decay  of  nitrogenous  substances.  The  decay  of 
nitrogenous  bodies,  especially  if  they  are  in  bulk,  is  usually  called 
putrefaction  because  much  of  the  process  of  decay  is  carried  on  in 
the  absence  of  air  by  anaerobic  bacteria,  and  among  other  products 
foul  smelling  gases  are  evolved.  These  processes  of  decay  so 
often  destructive  of  economic  products,  and  which  modern  indus- 
trial development  has  done  much  to  prevent  as  applied  to  food 
products  for  man,  are  really  of  the  greatest  importance  and  value 
viewed  from  the  standpoint  of  economy  in  nature.  All  dead 
plants  and  animals  left  to  the  operation  of  nature's  laws,  by  the 
action  of  a  long  series  of  organisms,  are  finally  reduced  to  a  condi- 
tion in  which  they  can  be  used  as  food  by  the  higher  plants  again, 
thus  perpetuating  life,  through  the  decay  of  the  dead,  and  the 
endless  circulation  of  food  substances.  Some  of  these  processes 
cf  decay  are  useful  in  preparing  certain  foods.  Cream  is  "  rip- 
ened "  for  butter  by  the  action  of  special  bacteria.  The  great 
variety  of  cheeses  with  their  distinct  flavors  and  odors  is  made 
possible  by  the  action  of  specific  kinds  of  fungi.  Fresh  meats  are 
made  more  tender  and  to  some  more  palatable  after  a  process  of 
"  ripening,"  which  is  in  reality  an  incipient  decay.  Very  poison- 
ous products  called  ptomaines  are  sometimes  formed  in  fish  and 
other  meats  as  a  result  of  incipient  decay  by  bacteria  which  cause 
serious  illness  and  sometimes  death  to  those  who  eat  them. 

218.   Fermentation. — Fermentation    is    really    a   process    of 
decay.     Starch  can  be  fermented   into   sugar   by  certain  fungi. 


134  GROWTH   AND    WORK   OF  PLANTS 

Sugars  are  fermented  into  alcohol  and  carbon  dioxide.  Alcoholic 
fermentation  is  caused  by  the  action  of  yeasts  on  carbohydrates, 
and  yeasts  are  employed  in  the  commercial  process  of  brewing 
beer.  The  same  yeasts  are  also  used  in  bread  making.  When 
the  "dough"  is  set  aside  to  "  rise,"  the  yeast  plant  in  the 
"yeast"  which  is  added,  ferments  the  sugar  into  alcohol  and 
CO2o  The  latter  being  a  gas  forms  gas  cavities  in  the  dough 
which  causes  the  bread  to  "  rise."  It  is  then  placed  in  the 
oven,  the  heat  expands  the  gas  and  causes  the  bread  to  "rise" 
still  more  so  that  it  becomes  "light"  and  the  baking  makes 
the  loaf  rigid  in  this  form.  Acid  fermentation  is  another 
kind  of  fermentation  caused  by  bacteria.  Alcohol  is  fermented 
by  the  acetic  acid  bacteria  into  acetic  acid.  This  process 
takes  place  in  the  making  of  vinegar  from  cider.  The  lactic 
acid  bacteria  (Bacillus  acidi  lacti)  cause  the  souring  of  milk. 
Sugar  and  cellulose  can  also  be  fermented  into  butyric  acid  by 
certain  bacteria. 

210.  Unorganized  ferments. — The  yeasts  and  bacteria  which 
produce  fermentation  are  called  organized  ferments,  since  they 
are  living  organisms.  There  is  another  kind  of  fermentation 
caused  by  what  are  termed  unorganized  ferments.  These  are 
usually  known  as  enzymes  or  diastases.  They  are  substances  pro- 
duced in  different  parts  of  plants  and  animals  which  act  on 
starch  and  other  substances  in  such  a  way  as  to  digest  or  dis- 
solve them.  A  well-known  animal  diastase  (ptyalin)  is  present  in 
the  saliva  of  the  mouth,  which  is  necessary  as  one  step  in  the 
digestion  of  starch  by  animals,  thus  the  importance  of  thorough 
mastication  of  the  food  to  mix  the  saliva  with  it.  Leaf  diastase 
is  formed  in  the  leaves  of  green  plants  to  change  the  starch 
formed  during  the  day  into  sugar  so  that  it  can  be  transported 
to  other  parts  of  the  plant.  Malt  diastase  is  formed  in  seeds  and 
is  especially  abundant  in  barley  which  is  used  to  make  "  malt"  in 
the  breweries.  The  diastase  dissolves  the  starch  to  sugar,  and  then 
the  yeast  (an  organized  ferment)  ferments  the  sugar  to  alcohol. 
Taka  diastase  is  a  special  diastase  formed  by  a  mold  fungus 
(Aspergillus  oryzae)  which  grows  on  rice  grains.  The  fungus 


NUTRITION  OF  PARASITES  AND  SAPROPHYTES       13$ 

excretes  the  diastase,  which  acts  on  the  starch  in  the  rice,  convert- 
ing it  into  sugar.  Taka  diastase  is  very  powerful  and  abundant. 
It  is  extracted  from  the  fungus  and  sold  for  medicinal  purposes. 
It  is  used  by  people  who  have  weak  digestion  to  aid  in  the  digestion 
of  starchy  foods.  Many  of  the  plant  diastases  are  very  powerful; 
a  small  quantity  can  dissolve  a  great  deal  of  starch  without  in 
the  least  diminishing  its  activity.  Recent  investigations  tend  to 
show  that  a  diastase  (called  zymase)  is  produced  by  the  yeast 
plant,  which  is  the  active  agent  in  the  alcoholic  fermentation  of 
sugar,  and  it  would  appear  that  there  is  not  such  a  great  differ- 
ence between  organized  and  unorganized  ferments,  for  it  may  be 
found  that  the  active  principle  in  all  so-called  organized  ferments 
is  an  unorganized  ferment  or  enzyme.  Oil  products  in  seeds,  etc., 
are  rendered  available  for  plant  food  by  a  ferment  called  lipase, 
cellulose  (in  some  seeds)  by  a  ferment  called  cytase,  proteid 
bodies  by  ferments  called  proteases,  and  albuminoids  by  a  tryptic 
ferment. 

BACTERIA. 

220.  The  bacteria  are  very  minute  plants,  some  of  them  the 
smallest  known  organisms.  Like  the  fungi  they  lack  chlorophyll, 
and  derive  their  carbohydrate 
food  from  living  or  dead  organ- 
isms or  from  organic  matter, 
since  they  are  not  able  them- 
selves to  fix  carbon  from  the 
carbon  dioxide  of  the  air  ex- 
cept in  a  few  forms  like  the 

nitrite  and  nitrate  bacteria  (see  threads,  unstained  roS,  and  stained  rodsSowing 

i  \       rr>i  n  cilia;  B,  Bacillus  tetani,   the  tetanus  or  lockjaw 

paragraph  20O).      1  hey  USUally  bacillus,  found  in  garden  soil  and  on  old  rusty 

•   ,        r  i  n        •  ,!  nails.      Spores  in  clubshaped  ends.     C,  Micro- 

COnSlSt    of    a    Single    Cell    With  coccus;  £>,  Sarcina;  E,  Streptococcus;  F,  Spiril- 

cell  wall  enclosing  the  proto-    lum"  (Aftei 

plasm.  In  form  they  are  rod-like  (Bacillus,  Bacterium),  thread-like 
and  formed  of  many  rod-like  segments  (Beggiotoa),  in  the  form  of 
a  screw  or  spiral  (Spirillum),  spherical  and  single  (Micrococcus), 
or  a  number  of  spheres  in  a  chain  (Streptococcus),  or  with  the 
spheres  in  groups  of  four  (Sarcina).  They  usually  multiply  by 


136  GROWTH   AND    WORK   OF  PLANTS 

division,  each  cell  dividing  into  two  equal  parts.  This  is  called 
multiplication  by  fission,  which  means  a  cutting  in  two.  For  this 
reason  they  are  sometimes  called  fission  fungi.  In  reproduction 
many  of  the  bacteria  form  spores,  the  protoplasm  condensing 
inside  the  cell  into  a  small,  rounded,  shining  body  which  is  much 
more  resistant  to  dessication,  heat,  cold,  and  the  action  of  poison- 
ous substances  than  are  the  vegetative  cells,  some  being  able  to 
resist  the  heat  of  boiling  water  for  several  minutes. 

The  bacteria  live  within,  or  upon  the  surface  of,  the  substance 
upon  which  they  feed.  Their  method  of  nutrition  is  similar  to 
that  of  the  fungi.  They  absorb  solutions  of  food  substances 
through  their  cell  walls.  The  bacteria  are  "  omnipresent,"  and 
being  very  minute  and  capable  of  rapid  multiplication  they  exist 
in  marvellous  numbers.  Some  species  multiply  so  rapidly  as  to 
produce  new  individuals  in  a  half  hour.  They  and  their  spores 
are  easily  carried  about  on  floating  particles  of  dust,  on  the  cloth- 
ing, the  hands  and  other  parts  of  the  body,  and  by  insects  and 
other  animals.  They  exist  in  the  mouth,  in  the  stomach  and 
throughout  the  intestinal  canal.  Fortunately  the  larger  number 
of  bacteria  are  harmless  and  many  are  beneficial,  as  we  have 
seen  in  the  study  of  decay,  nitrification,  fermentation,  fixation  of 
nitrogen,  etc.  (Chapter  XIV). 

231.  Diseases  caused  by  bacteria. — There  are,  however,  a 
number  of  diseases  of  both  plants  and  animals  caused  by  bac- 
teria. Among  plant  diseases  caused  by  bacteria  are  the  follow- 
ing: pear  blight,  or  fire  blight  of  the  pear,  apple  and  other  fruit 
trees  (killing  flowers,  leaves,  twigs  and  branches);  black  rots  of 
cabbage,  rots  of  turnip,  potatoes,  etc.,  bacteria  also  attack  the  leaves 
and  fruit  of  beans,  cotton;  some  cause  the  plants  to  wilt,  as  in 
melon  and  cucumber  wilt;  and  some  produce  galls  or  tubercular 
swellings  on  the  affected  parts,  as  on  the  olive  tree. 

222.  The  most  serious  diseases  caused  by  bacteria  are  those 
of  man  and  other  animals.  Because  of  the  small  size  of  the 
bacteria  they  are  often  spoken  of  as  germs,  and  the  diseases  they 
cause,  as  germ  diseases.  Some  of  these  diseases  are  as  follows: 
Typhoid  fever  caused  by  Bacillus  typhosus  in  the  alimentary  canal, 


NUTRITION  OF  PARASITES  AND  SAPROPHYTES 

consumption  or  tuberculosis  caused  by  B.  tuberculosus  in  the 
lungs  and  other  parts  of  the  body,  diphtheria  caused  by  B.  diph- 
theria, lockjaw  or  tetanus  caused  by  B.  tetani.  This  last  or- 
ganism is  abundant  in  cultivated  soil  and  on  old  rusty  nails. 
When  deep  wounds  in  the  flesh  are  caused  by  punctures  with 
objects  carrying  the  germs,  because  of  the  character  of  the  wound 
the  air  is  excluded.  Bacillus  tetanus  is  an  anaerobe  and  can  only 
grow  and  produce  the  tetanus  symptoms  in  the  absence  of  oxygen. 
Opening  such  a  wound  to  admit  air,  and  disinfecting  it  with  a 
weak  solution  of  bichloride  of  mercury  will  prevent  its  action. 
Other  bacterial  diseases  are  pneumonia,  influenza  or  la  grippe, 
anthrax,  swine  plague,  etc.  Many  of  these  bacteria  develop 
and  excrete  toxic  substances  called  toxins,  which  are  very 
poisonous.  These  act  locally  on  the  tissues,  and  in  many  cases, 
as  in  diphtheria,  are  carried  in  the  blood  to  all  parts  of  the 
system  and  cause  the  fever  in  the  patient.  The  bacteria  them- 
selves are  in  a  number  of  cases  finally  checked  in  their  growth  or 
killed  by  these  same  toxins  which  they  excrete.  This  principle 
has  led  to  an  important  practice  in  the  prevention  and  cure  of 
some  of  these  diseases,  i.e.,  by  injecting  what  is  called  an  antitoxin 
into  the  blood.  In  the  case  of  smallpox  the  bacteria  are  inocu- 
lated into  healthy  cows  and  a  mild  form  of  the  disease  is  developed. 
To  prevent  smallpox  in  man  some  "  virus  "  of  the  "  cow  pox  " 
is  then  inoculated  into  the  system,  or  the  person  is  vaccinated. 
The  result  is  a  very  mild  form  of  the  disease  and  the  system  is  able 
to  resist  it.  But  the  distribution  of  the  toxin  in  the  system  renders 
the  person  immune  from  the  disease  even  in  a  virulent  form  for 
a  number  of  years.  So  in  the  case  of  certain  contagious  diseases, 
as  in  cholera,  if  the  patient  recovers  he  is  immune  from  the  disease 
for  a  period  of  years. 

In  the  case  of  diphtheria  the  antitoxin  is  obtained  from  the 
blood  of  healthy  horses  in  the  following  way.  The  toxin  is  first 
obtained  from  pure  cultures  of  virulent  forms  of  the  bacillus. 
Successive  subcutaneous  injections  of  this  toxin  are  made  in  the 
horse  every  5  to  7  or  3  to  7  days  for  a  period  of  about  three  months 
when  blood  is  drawn  from  the  jugular  vein  of  the  horse,  allowed 


138  GROWTH   AND    WORK   OF  PLANTS 

to  clot  and  the  antitoxic  serum  is  withdrawn.  Successive  injec- 
tions are  made  up  to  about  nine  months  and  blood  is  drawn  from 
the  horse  from  time  to  time.  The  horse  may  then  be  given  a  rest 
for  a  few  months  and  used  again.  In  recent  years  it  is  customary 
to  inject  antitoxin  into  the  horse  along  with  the  first  doses,  since 
a  much  larger  dose  of  toxin  can  be  administered  and  the  process 
of  making  the  desired  strength  of  antitoxin  is  accelerated.  The 
antitoxin  is  injected  into  the  patient  suffering  from  diphtheria  in 
an  early  stage  of  the  disease.  This  antitoxin  checks  the  growth 
of  the  bacillus  and  the  disease  runs  its  course  in  a  much  milder 
form. 

223.  Public  duty  in  the  preservation  of  health. — With  the 
knowledge  gained  in  the  investigations  as  to  the  cause,  prevention 
and  treatment  of  these  germ  diseases,  it  becomes  the  public  duty 
of  every  person  to  be  familiar  with  the  principal  facts  as  to  the 
cause  of  disease,  the  means  of  infection  and  contagion,  and  to 
use  every  care  not  only  in  the  preservation  of  his  own  health  but 
in  preventing  the  distribution  of  the  germs  which  will  communicate 
the  disease  to  others.  It  is  well  known,  for  example,  that  the 
typhoid  fever  germs  are  taken  into  the  system  by  drinking  con- 
taminated water  or  milk  or  by  eating  contaminated  food.  The 
great  epidemics  of  typhoid  fever,  where  they  have  been  traced,  have 
been  found  to  originate  from  one  or  two  isolated  cases  on  the  water 
shed  of  the  public  water  supply.  Carelessness  in  throwing  the 
refuse  from  a  patient  where  rains  or  melted  snows  carry  the  bac- 
teria into  the  water  supply  has  often  resulted  in  an  epidemic,  since 
many  of  those  drinking  from  the  public  supply  contract  the 
disease.  All  such  refuse  matter  should  be  thoroughly  disinfected 
and  then  covered  where  there  wrill  be  no  drainage  into  streams, 
for  even  if  it  is  not  drained  into  a  water  supply,  flies  during  the 
warm  season  will  carry  on  their  legs  myriads  of  the  germs  and 
then  deposit  them  on  food.  The  hands  of  attendants  as  well  as 
other  things  in  the  sick  room  should  be  properly  disinfected,  since 
contact  of  these  with  food  or  fruits  or  with  vessels  used  for  holding 
milk  or  food  leads  to  the  contamination  of  these  substances. 
Nearly  every  typhoid  epidemic  shows  two  sources  of  infection,  the 


NUTRITION  OF  PARASITES  AND  SAPROPHYTES       139 

"  original  one  from  the  water  supply,  and  then  a  number  of  second- 
ary ones  around  the  various  primary  cases  due  to  carelessness 
in  or  lack  of  proper  disinfection.  Boiling  the  water  or  milk  and 
thoroughly  cooking  the  food  kills  the  germs,  but  the  wiser  way 
is  to  prevent  the  primary  infection.  In  this  respect  the  public 
authorities  should  see  to  it  that  the  water  supply  is  kept  pure  both 
by  cleanliness  of  the  water  shed,  and  by  building  proper  nitration 
plants  where  a  supply  of  pure  artesian  water  is  not  available. 


CHAPTER   XVI. 


FLOWERS,  THEIR  STRUCTURE  AND   KINDS. 

IN  some  of  the  preceding  chapters  all  parts  of  the  plant  have 
been  studied  except  the  members  of  the  flower  shoot  which  will 
be  studied  now. 

224.  The  flower  is  not  only  a  very  interesting,  usually  beauti- 
ful and  conspicuous  part  of  the  plant,  but  it  is  a  very  import- 
ant structure.  The  chief  end  towards  which  the  plant  works 

is   the    production    of 

seed  or  some  other 
structure  of  similar 
function,  for  the  mul- 
tiplication of  its  kind. 
The  flower  performs 
a  very  important  work 
in  the  production  of 
seed.  The  seed  is 
formed  in  certain  parts 
of  the  flower.  The 
organs  concerned  in 
the  process  of  pollina- 
tion and  fertilization, 
which  are  necessary 
(except  in  very  rare 
cases)  for  the  develop- 

Flg.  102. 

Flower  cluster  of  Rhododendron  maximum.  ment    of    the    Seed,  are 

formed   in  the   flower 

or  have  a  very  intimate  nutritive  dependence  on  some  of  its 
parts.  Many  flowers  have  certain  conspicuous,  often  beauti- 
fully colored  members,  which,  it  is  believed,  attract  insects  that 
aid  in  pollination.  Other  members  are  present  in  most  flowers 

140 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS        14! 

which  serve  the  purpose  of  protecting  the  essential  members  con- 
cerned in  pollination  and  seed  production  while  they  are  in  a 
young  and  tender  condition,  in  the  bud. 

225.  The  members,  or  parts,  of  the  flower  are  crowded 
together  on  a  very  short  portion  of  the  stem.     This  close  asso- 
ciation of  a  number  of  such  important  parts  of  a  plant  into  one 
structure  gives  a  very  great  importance  to  the  flower  in  indi- 
cating the   relationships  of   flowering  plants.     While   there   are 
other  parts  of  flowering  plants  which  are  of  importance  in  show- 
ing relationships,  the  flower  is  one  of  the  most  important  struc- 
tures in  this  respect.     In  addition  to  the  complex  structure  of 
the   flower  already  indicated,  when  we   come   to   compare  the 
flowers  of  different  kinds  of  plants  we  find  that  the  members  of 
the  flowers  vary,  not  only  in  the  number  of  the  different  kinds  of 
members  and  their  form,  but  in  the  relation  of  the  kinds  of  mem- 
bers among  themselves  and  to  each  series  of  members.     In  the 
simpler  kinds  of  flowers  the  members  are  all  separate  and  dis- 
tinct, while  in  the  more  complex  and  highly  developed  ones  the 
members  are  more  or  less  united.     It  is  important  therefore  in 
the  study  of  flowers  that  we  should  attempt  to  determine  not 
only  the  parts  which  are  present,  their  position,  and  relation  to 
each  other,  their  function,  the  different   mechanisms  by  which 
the  different  kinds  of  flowers  perform  their  functions,  but  also 
the  significance  of  the  form  of  the  flowers  and  their  arrange- 
ments on  the  flower  shoot. 

226.  The  different  kinds  of  members,  or  parts,  of  the  flower 
appear  to  be  arranged  in  whorls,  because  they  are  so  closely 
crowded  on  the  stem.     In  some  flowers,  the  buttercup  and  some 
of  its  relatives,  they  are  believed  to  be  arranged  in  spirals  similar 
to  the  arrangement  of  the  leaves,  though  so  crowded  that  it  is 
difficult  to  determine. 

Studies  of  a  few  flowers  are  presented  here  to  illustrate  their 
structure,  ?s  well  as  the  arrangement  and  relation  of  their  parts. 


142 


GROWTH   AND    WORK   OF   PLANTS 


I.    FLOWERS    OF    DICOTYLEDONOUS  PLANTS. 

The  Buttercup. 
(Ranunculus.} 

227.  Almost  any  of  the  species  of  buttercup  will  answer  for 
the  study  of  the  flower.  This  study  is  made  from  the  tall  or 
meadow  buttercup.  It  is  common  in  fields  and  roadsides, 
especially  in  the  Northern  States  and  Canada,  from  May  to  Sep- 
tember. The  flowers  are  bright  yellow  and  are  borne  two  or 
three  or  more  in  loose  corymbs. 


Fig.  103. 

Flower  of  buttercup  (Ranunculus  acris)  with  petals  removed  and  arranged  at  left. 
flower  at  the  right  has  the  sepals,  stamens  and  pistils. 


The 


228.  The  calyx.—  The  outer  whorl  of  members  of  the  flower 
is  the  calyx.  In  the  buttercup  the  calyx  consists  of  five  distinct 
members.  Each  member  or  part  of  the  calyx  is  known  as  a 
sepal.  In  the  meadow  buttercup  the  sepals  are  elliptical  in  form 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS         143 

and  greenish.  They  fall  away  very  easily  and  it  is  necessary  to 
examine  young  flowers  to  see  them.  The  calyx  serves  the  pur- 
pose of  protecting  the  other  members  of  the  flower  in  the  bud. 

229.  The  corolla. — Next  inside  of  the  calyx  is  the  corolla.     It 
consists  of  five  distinct,  free  members  or  parts,  of  bright  yellow 
color.     Each  one   of   these   is   a  petal.     The   number  of  petals 
sometimes  varies,  six  sometimes  being  present.     Each  petal  is 
broadly  obovate,  wedge-shaped  in  outline,  with  a  minute  claw  at 
the  base  on  the  upper  side.     The  function  of  the  corolla,  when 
bright  in  color,  is  supposed  to  be  that  of  attracting  insects  which 
aid  in  pollination.     It  also  serves  to  protect  the  inner  members  of 
the  flower  in  the  bud. 

230.  The  stamens. — Just  inside  of  the  corolla  are  a  large 
number   of    small    flower    members    known    as    stamens.     Each 
stamen  consists  of  two  parts,  the  stalk  or  filament,  and  a  broad 
terminal  portion,  the  anther.     The  anther  is  slightly  lobed  into 
two  parts.     Each  lobe  is  called  an  anther  sac,  or  locule.     It  is  a 
little  case,  containing,  when  ripe,  the  pollen  grains,  very  small, 
free  cells,  which  are  produced  in  great  numbers.     In  the  butter- 
cup these  lobes  open  by  splitting  along  the  middle  line  on  one 
side,  and  permit  the  scattering  of  the  pollen  which  to  the  eye 
resembles  a  fine  grained  powder.     The  filament  of  the  stamen  is 
attached  along  the  inner  face  of   the 

anther,  and  the  latter  in  such  a  case 
is  said  to  be  adnate. 

231.  The  pistils. — The  pistils  are 
the  members  which  occupy  the  center 
or  summit  of  the  flower.      They  are 
numerous  and  distinct  from  each  other. 

The  pistil  is  recognized  as  consist- 
ing of  three  parts,  the  ovary,  the  style  Young  fruit^'bmLcup  (R.  acris) 
and  the  stigma.  The  ovary  is  the 
lower  and  larger  part.  It  is  ovate  in  showmg  position  °\ ovule- 
outline  and  compressed.  The  ovary  is  hollow,  and  by  cutting  off 
one  side,  a  small  body  is  seen  which  is  attached  at  the  base. 
This  is  the  ovule  in  which  the  embryo  plan?  is  formed  after 


144 


GROWTH   AND    WORK   OF   PLANTS 


fertilization,   the  ovule   and  embryo  together  making  the  seed. 

The  style  is  the  short,  slender  portion  of  the  pistil,  and  bears  the 

stigma  at  its  apex.  When  the 
seed  ripens  the  ovary  remains 
closed  and  firmly  surrounds 
the  seed.  This  forms  a  one- 
seeded  fruit,  which  is  known 
as  an  akene. 

232.  A   flower    like    the 
buttercup,  which    has    all 
four  series  of  members,  is 
called  a  complete  flower,  and 
because  it  has  both  stamens 
and  pistils  it  is  known  as  a 
perfect    flower.     Because    the 
petals  are  distinct  from  each 
other  it  is  called  polypetalous, 
i.e.,  having  many  petals.    Be- 
cause all  of  the  parts  are  free 
and  distinct  (that  is,  not  joined 
to  ether  members,  or  to  mem- 
bers of  the  same  set  or  whorl) 
it  is  a  simple  flower. 

233.  The    part     of    the 
flower  to  which  these  differ- 
ent members  are  attached  is 
the  receptacle.    The  receptacle 
is  a  more  or  less   broadened 
part  of  the  stem.     It  has  not 
elongated,  and  thus  the  mem- 
bers of  the  flower,  which   belong  to   the   same   series  of  plant 
parts  as  the  leaves,  are  very  much  crowded.     The  pistils  being 
in  the  center  of  the  flower,  therefore  stand  highest  upon  the  stem, 
that  is,  at  its  apex.     All  the  other  members  of  the  buttercup 
flower  are  successively  below  the  pistil  and  are  therefore  said  to 
be  hypogenous,  i.e.,  underneath  the  pistil. 


Fig.  105. 

Flower  shoot  of  evening  primrose  (CEnothera 
biennis).  Flower  buds  at  apex,  opening 
flowers  next,  and  fruits  forming  below.  Inde- 
terminate inflorescence. 


FLOWERS,    THEIR  STRUCTURE  AND   KINDS         14$ 


The  Evening  Primrose. 
((Enothera  biennis  =  Onagra  biennis.) 

234.  The  flowers  of  -the  evening  primrose  are  formed  in  a 
rather  loose  spike,  which  continues  to  grow  at  the  end,  producing 
new  flowers  in  the  axils  of  the  bracts,  while  the  seed  is  ripening  in 
the  lower  older  fruit  pods.     In  vigorous  plants  flower  spikes  are 
also  formed  on  the  branches  in  the  axils  of  the  upper  leaves. 

235.  The  calyx  forms  a  long  tube,  the  lower  part  of  which  is 
joined  to  (adnate)  the  outside  of  the  ovary.     This  tube  is  pro- 
longed far  above  the  apex  of  the  ovary  and  is  about  twice  the 
length   of   the   young  ovary.     The 

free  part  of  the  tube  is  easily 
distinguished  from  the  part  adnate 
with  the  ovary  by  its  light  green 
color.  The  calyx  lobes  are  four 
in  number,  long,  narrowly  acu- 
minate, and  in  the  flower  bud 
the  edges  fit  closely,  giving  the 
bud  an  elongate,  four-angled, 
pointed  form.  These  calyx  lobes 
are  the  free  parts  of  the  sepals,  the 
edges  of  which  are  united  below  to 
form  the  tube.  As  the  flower  opens 
the  calyx  lobes  part,  and  become 
inverted,  hanging  downward  from 
the  apex  of  the  tube. 

236.  The  corolla  is  bright  yel- 
low and  consists  of  four  petals  which  the  long  style> 

are  inserted  on  the  edge  of  the  calyx  tube.  Each  petal  is  broadly 
wedge-shaped  and  notched  in  the  free  end,  or  rather  it  is  heart- 
shaped.  The  petals  are  convolute  in  the  bud,  as  shown  in  fig.  108, 
where  they  are  just  unfolding. 

237.  The  stamens  are  eight  in  number,  seated  also  on  the 
edge  of  the  calyx  tube  and  partly  on  the  base  of  the  petals  since 


Fig.  106. 

Flower  of  evening  primrose  (OZ.  bien- 
nis) with  corolla  tube  split  open  to  show 


146  GROWTH   AND    WORK   OF   PLANTS 

the  stamen  sometimes  remains  attached  to  the  base  of  the  petal 
when  that  is  removed  from  the  calyx  tube.  Four  of  the  stamens 
are  set  opposite  the  petals  and  four  are  alternate  with  them  as 
shown  in  the  photograph  of  a  dissected  flower  in  figs.  106, 107.  The 


Fig.  107. 

Flower  of  evening  primrose  with  petals  removed  to  show  the  four  spreading  lobes  of  the 
stigma,  and  anthers  beneath  them.     Petal  at  right,  showing  two  stamens  attached. 

filaments  are  strongly  curved  at  the  base,  all  in  the  same  general 
direction,  with  the  concavity  toward  the  axis  of  the  spike.  The 
anthers  are  versatile,  i.e.,  each  anther  is  attached  by  one  face 
near  the  middle  to  the  point  of  the  filament,  upon  which  it  swings 
loosely.  The  filament  is  attached  to  the  outer  face  of  the  anther, 
so  that  the  anther  faces  inward  toward  the  axis  of  the  flower,  and 
is  said  to  be  introrse,  or  incumbent.  The  anther  consists  of  two 
pollen  sacs  (locules)  which  open  by  a  long  slit  on  the  inner  faces. 
This  takes  place  before  the  flower  opens  and  the  pollen  is  depos- 
ited in  great  masses  on  the  outer  surfaces  of  the  four  lobes  of  the 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS         147 


stigma.  The  stigmatic  surface  is  on  the  inner  face  of  the  stigma 
lobe  and  is  not  yet  mature,  so  that  the  pollen  from  the  anthers  of 
this  flower  cannot  usually  bring  about  fertilization  in  this  flower. 
Insects  which  visit  this 
flower  carry  the  pollen  to 
another  flower  where  the 
stigma  lobes  are  mature, 
open  and  spreading. 
They  are  thus  ready  to 
receive  the  pollen  brought 
by  the  insect  from  the 
former  flower.  This 
mechanism  of  the  flower 
necessitates  cross-pollina- 
tion for  the  production  of 
an  abundance  of  seed  (see 
chapter  on  Pollination). 

238.  The     pollen 
grains   are   loosely   held 
together   by  delicate 
"cobwebby"  threads,  and 
the  mass  is  slightly  sticky, 
so  that  it  adheres  readily 
to    objects   which    it 
touches.     These   delicate 
threads,    shown    in    the 

photograph,  fig.  109,  are  probably  formed  by  the  partial  gelatini- 
zation  and  shredding  of  the  outer  layer  of  the  walls  of  the  pollen 
grains.  Each  pollen  grain  is  strongly  three-angled,  the  angles 
appearing  as  pronounced  protuberances,  each  one  nearly  as  large 
as  the  central  body.  Germination  of  the  pollen  grains  takes 
place  through  these  angles. 

239.  The  pistil  of  the  evening  primrose  consists  of  three  dis- 
tinct parts,  the  ovary,  the  style,  and  the  four  stigmas.     The  ovary 
is  at  first  nearly  cylindrical,  but  becomes  four-angled  with  the 
ripening  of  the  seed.     The  ovary  consists  of  four  locules.     This 


Fig.  108. 

Flowers  of  evening  primrose,  the  two  at  left  showing 
the  way  the  petals  are  folded  in  the  bud.  At  the  right, 
petals  removed,  showing  anthers  opening  while  the 
stigma  lobes  are  still  closed. 


148 


GROWTH   AND    WORK   OF   PLANTS 


indicates  that  it  is  composed  of  four  parts  which  are  united  to 
form  a  compound  ovary.  The  ovules  are  numerous  and  occur 
in  two  rows.  The  style  is  longer  than  the  calyx  tube  and  is  well 
shown  in  the  dissection  of  the  flower.  The 
stigma  consists  of  four  short,  nearly  cylin- 
drical lobes  at  the  apex  of  the  style.  In 
the  flower  bud  these  are  erect,  approximate, 
and  project  a  little  above  the  convolute 
petals.  Here  the  inner  faces  of  the  anthers 
are  pressed  closely  against  the  lower  half 
of  the  outer  face  of  the  stigmas  and  deposit 
the  pollen  on  them  as  described  above. 

The  four  parts  of  the  ovary  and  the  four 
lobes  of  the  stigma  indicate  that  the  pistil  is 
madeupof  four  parts,  or  carpels,  which  have 
become  united  into  one  compound  pistil. 
All  of  the  parts  of  the  flower,  therefore, 
of  the  evening  primrose  are  m  fours. 

240.    One  species  of  the  evening  prim- 
^^j^^H^*  rose,    (Enothera    lamarkiana    (Lamark's 

.^"MR  evening  primrose),  has  become  celebrated 

I^Hf  through   the    experiments   of   the    Dutch 

Pfl  botanist,   DeVries,  for  the  sudden  varia- 

4IPP  tions  which  appear  in  plants  grown  from 

the  seed,  giving  rise  to  distinct  forms. 
These  forms  are  regarded  as  elementary 
species,  and  as  indicating  one  method  of 
the  evolution  of  new  species. 


Fig.  109. 

Photomicrograph  of  pollen 
of  evening  primrose,  showing 
threads  which  hold  the  grains 
in  loose  masses. 


Butter  and  Eggs. 
(Linaria  vulgaris  =  Linaria  linaria.) 

241.  This  plant  occurs  by  roadsides  and  in  waste  places.  It 
is  from  one  to  nearly  three  feet  high  (3-9  decimeters),  branched, 
with  linear  leaves.  The  leaves  are  mostly  alternate,  but  are  often 
grouped  on  the  stem,  two,  three,  or  four  arising  close  together 
on  the  stem  and  almost  opposite  or  verticillate. 


FLOWERS,    THEIR  STRUCTURE  AND   KINDS         149 

242.  The  flowers  are  in  dense  terminal  racemes,  with 
pedicels  3  to  5  mm.,  each  flower  arising  in  the  axil  of  a  slender 
acuminate  green  bract.     The  white  or  greenish-white   flowers, 
with  the  orange  yellow  "  palate  "  of  the  corolla,  are  very  striking 
and  gave  rise  to  the  name  "  butter  and  eggs." 

243.  The  calyx  consists  of  five  sepals,  which  are  green,  nor- 
mally acuminate  and  coalesced  at  the  base  by  their  edges.     When 
the  sepals  are  coalesced  the  calyx  is  said  to  be  gamosepalous. 
Here  it  is  deeply  divided  into  five  lobes  showing  clearly  the  five 
sepals. 

244.  The  corolla  is  irregular,  that  is,  the  petals  or  their  lobes 
are  of  unequal  size.     The  petals  are  coalesced,  and  the  corolla  is 


Fig.  no. 
Flower  detail  of  "butter  and  eggs"  (Linaria  vulgaris). 

therefore  gamopetalous.  The  corolla  is  also  two-lipped  (bilabiate), 
as  can  be  plainly  seen  from  a  side  view.  The  two  upper  petals 
form  the  upper  lip,  and  a  short  notch  or  incision  indicates  the  two 
petals.  The  lower  lip  consists  of  three  petals  which  are  indicated 
by  the  lobes,  two  broad  outer  ones  and  a  smaller  middle  one. 


150  GROWTH   AND    WORK   OF  PLANTS 

The  lower  part  of  this  lip  is  prolonged  into  a  long  straight  spur. 
The  upper  part  of  the  lower  lip,  at  the  point  to  which  the  incision 
extends  that  indicates  the  lobes,  is  of  a  deep  orange  color  and 
arched  upward  so  that  it  closes  the  "  throat  "  of  the  corolla.  This 
is  called  the  palate,  and  when  at  rest  it  closes  the  throat.  By 
pulling  apart  on  the  two  lips  the  throat  is  exposed,  and  at  the  same 
time  it  is  seen  that  the  incision  which  separates  the  two  lips  is 
much  deeper  than  those  which  separate  the  petal  lobes  of  each  lip. 

245.  The  stamens  are  four  in  number  and  are  seated  on  the 
corolla  near  the  base  of  the  broad  part  of  the  throat  around  the 
ovary.     The  stamens  are  of  two  forms  (dimorphic),  the  two  lower 
ones  being  shorter  than  the  upper  ones.     They  are  shown  in 
fig.  no  attached  to  the  base  of  the  corolla  tube,  the  corolla  having 
been  removed  from  the  receptacle  and  the  lower  lip  cut  away. 
The  anther  lobes  are  two  in  number  and  nearly  confluent  at  one  end, 
where  the  filament  is  inserted  between  them,  and  diverge  some- 
what from  this  point.     Each  locule  opens  by  a  longitudinal  slit 
along  the  inner  face,  the  face  opposite  to  the  attachment  of  the 
filament. 

246.  The  pistil  is  single  and  entire.     The  ovary  is  superior 
oval  in  shape  and  two-loculed.     There  is  a  thickened  placenta  on 
either  side  of  the  partition  which  is  covered  with  numerous  ovules 
which  fill  the  locules.     The  style  is  simple,  short  filamentous  and 
slightly  enlarged  at  the  end,  the  upper  surface  being  the  stigma. 

The  Sweet  Pea. 

247.  The  flowers  of  the  sweet  pea  are  produced  singly  or 
in  loose  clusters  of  two  or  three  on  long  flower  stems  or  peduncles. 
The  calyx  is  regular,  gamosepalous,  green,  and  divided  into  five 
even  or  nearly  even  pointed  lobes  which  represent  the  sepals. 
It  is  inferior. 

248.  The  corolla  is  irregular  and  peculiar  in  form,  said  to  be 
butterfly-shaped  (papilionaceous).     The  upper  petal  is  the  broader 
one,  nearly  rounded  and  with  a  short  limb.     It  usually  stands 
erect,  and  is  known  as  the  "  banner  "  or  "  standard."    The  two 
lateral  petals  are  irregularly  wedge-shaped,  and  are  forked  at  the 


FLOWERS,    THEIR  STRUCTURE  AND    KINDS        151 

smaller  end  (said  to  have  two  claws).  These  two  petals,  because 
of  their  position,  are  inown  as  the  "  wings  "  or  alee.  The  two 
front  petals  are  par- 
tially united  into  one 
in  the  shape  of  a 
curved,  thin,  flat- 
tened body  which  is 
known  as  the 
"keel." 

249.  The  sta- 
mens are  ten  in  num- 
ber, and  are  in  two 
groups.  One  group 
consists  of  a  single 
stamen,  the  upper 
one.  The  other  nine  Fig-.T1;- 

Flowers  of  sweet  pea  in  front  and  side  view. 

are  joined  into  one 

group,  the  filaments  being  united  at  their  base  for  half  their  length 

and  closely  wrap- 
ped about  the 
small  flattened 
pod,  the  single  sta- 
men lying  at  the 
point  where  the 
edge  of  the  united 
filaments  ap- 
proach. When  the 
stamens  form  two 
groups  they  are 
said  to  be  diadel- 
phous  (i.e.,  of  two 
Fig.  1I2.  brotherhoods). 

Details  of  petals  of  sweet  pea  flower;  banner  above,  wings  at      The      anthers      are 
the  side,  keel  below.  -      ^ 

adnate,  two-lobed, 

each  lobe  having  one  locule,,  which  opens  by  #  longitudinal  cleft 
on  its  inner  face. 


152  GROWTH  AND    WORK   OF  PLANTS 

250.  The  pistil  is  simple.     The  ovary  is  flattened,  elongate, 
with  the  ovules  arranged  in  a  row  at  the  upper  edge.     It  forms 
the  pod,  or  legume.     The  style  is  slender  and  curved  upward, 
and  bears  the  stigma,  which  is  narrowly  elliptical  and  somewhat 
broader  than  the  style.     The  free  part  of  the  filaments  are  curved 
also  to  surround  the  style,  bringing  the  anthers  close  around  the 
stigma,  upon  which  the  pollen  is  shed  before  the  flower  opens,  so 
that  self-pollination  usually  takes  place. 

251.  This  type  of  flower,  called  papilionaceous  because  of 
its  resemblance  to  a  butterfly  (papilio),  is  characteristic  of  a  large 
number  of  plants  belonging  to  the  important  family  known  as 


Fig.  113- 

Flowers  of  sweet  pea,  corolla  removed.     Note  diadelphous  stamens,  one  single  one, 
the  others  all  united. 

the  pulse  family  or  pea  family  (Leguminosa,  sometimes  called 
Papilionacea),  including  the  peas,  beans,  clovers,  alfalfa,  etc. 
Besides  their  importance  as  food  for  man  and  animals,  they  play 
a  very  important  part  in  the  enrichment  of  the  soil  in  nitrogen 
through  the  nitrogen-fixing  bacteria  which  grow  as  parasites  in 
their  roots. 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS        153 

The  Sunflower. 
(Helianthus  annuus.} 

252.  The  sunflower  is  widely  cultivated  in  gardens  for  its 
showy  flower   head,   and   for   the   seed,  which  is  considered  a 
healthful  food  to    be  given   occasionally  to   poultry  and  stock. 
It  grows  wild  along  the  rich  river  valleys  in  some  of  the  Western 
States. 

The  sunflower  is  an  excellent  example  for  the  study  of  the 
type  of  flowers  which  form  a  head.  The  "  flower  head"  is  made 
up  of  a  large  number  of  flowers  crowded  very  closely  together  in 
a  rounded  or  flattened  group  on  the  broad  receptacle.*  Each 
one  of  these  flowers  is  called  &  floret.  In  the  sunflower  head  there 
are  two  kinds  of  flowers.  The  most  showy  flowers  in  the  head 
are  the  long  yellow  strap-shaped  ones  on  the  border  of  the  head, 
where  they  extend  outward  in  the  form  of  rays.  These  are 
called  ray  flowers.  The  disk  flowers  are  very  great  in  number 
and  occupy  the  space  inside  of  the  circle  of  ray  flowers.  The 
corolla  is  tubular  in  form,  and  the  disk  flowers  are  often  called 
tubular  flowers.  Each  disk  flower  grows  by  the  side  of  (really 
in  the  axil  of)  a  slender  pointed  bract.  On  the  outside  of  the 
head  are  a  large  number  of  overlapping  green  leaf -like  members, 
each  with  a  long,  narrow,  pointed  end.  These  are  bracts  which 
together  make  up  the  involucre,  which  encloses  the  head  in  the 
young  stage. 

253.  The  disk  flowers  or   tubular  flowers. — The  flowers 
should  be  studied  in  the  different  stages  of  flowering.     The  mode 
of  inflorescence  is  centripetal.      The  flowers  on  the  outer  margin 
of  the  disk  open  first,  while  those  in  the  center  are  still  quite 
young.     These  form  a  circle,  and  as  they  pass  the  height  of  the 
flowering  period  another  broad  circle  of  flowers  just  inside  the 
outer  ring  come   into   the   height  of   flowering.      The   circle   of 

*  Such  flowers  are  often  called  compound  flowers.  The  family  to  which 
the  sunflower  belongs  is  the  Composite,  and  its  members  are  often  spoken 
of  as  composites.  Besides  the  sunflower  it  includes  such  plants  as  the  golden- 
rod,  aster,  daisy,  yellow-eyed-susan,  dandelion,  chicory,  lettuce,  Joe-pye- 
weed,  chrysanthemums. 


154 


GROWTH   AND    WORK   OF  PLANTS 


flowers  in  the  height  of  flowering  is  always  very  conspicuous, 
because  the  stamens  and  the  stigmas  of  the  flower  project  so  far 
above  the  corolla  tube  at  this  time,  and  then  by  shortening 


Fig.  114. 
Tubular  flowers  of  sunflower,  showing  details  of  flowering  from  left  to  right. 

become  inconspicuous  again  (see  figs.  114,  115).  For  the  study 
of  the  flower  several  disk  flowers  in  different  stages  of  flowering 
should  be  separated  from  the  disk  for  close  examination. 

254:.  The  calyx. — The  calyx  is  very  inconspicuous.  The 
ovary  is  inferior  since  the  calyx  is  joined  to  its  outer  surface  and 
covers  it.  It  is  seen  as  a  narrow  wedge-shaped  white  body  with 
the  rest  of  the  flower  borne  on  its  apex.  The  calyx  is  manifest 
here  only  as  two  small  white  awn-like  lobes,  or  chaff,  which  are 
opposite  (sometimes  there  are  rudiments  of  smaller  ones  between). 

255.  The  corolla. — The  tubular  corolla  is  abruptly  broadened 
or  inflated  near  the  base.     The  apex  is  divided  into  five  short 
acute  lobes  which  show  that  it  is  composed  of  five  petals.     Com- 
pare this  inflated  portion  of  the  corolla  in  tubular  flowers  of 
different  ages. 

256.  The  stamens. — The  stamens  are  joined  together  by  the 
edges  of  their  anthers  and  are  thus  syngenesious.     They  are  five 
in  number  and  attached  by  the  filaments  to  the  lower  part  of  the 
inflated  portion  of  the  corolla.     The  anthers  thus  form  a  tube 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS        155 

which  surrounds  the  upper  part  of  the  style  and  the  stigma. 
They  open  by  their  inner  face,  shedding  the  pollen  on  the  hairy 
outer  faces  of  the  stigma. 

257.  The  pistil. — The  ovary  is  narrowly  wedge-shaped,  four- 
sided  by  compression.     The  style  is  long  and  slender,  and  the 
stigma  is  divided  longitudinally  into  two  portions.     The  inner 
plane  surfaces  fit  closely  together,  and  the  outer  hairy  surfaces 
are  in  contact  with  the  anther  locules  up  to   and  during  the 
early  stage  of  flowering. 

258.  Peculiarities  in  the  flowering  of  the  disk  flowers.— 
The  mode  of  inflorescence  is  centripetal  as  described  above,  i.e., 
it  proceeds  from  the  outside  inward.     At  the  time  of  flowering 
the  anther  tube  and  the  stigma  which  it  surrounds  are  pushed  out 
of  the  corolla  tube  by  the  gradual  elongation  of  the  filaments 
and  the  style,  though  the  anthers  are  often  slightly  in  advance  of 


Fig.  115. 

Section  through  head  of  sunflower,  showing  details  of  flowering  from  the  outside 
toward  the  center. 

the  stigma  (see  figs.  114,  115  for  details).  This  takes  place,  as  I 
have  observed  it,  during  the  night  and  early  morning.  In  the 
course  of  two  to  four  hours,  the  style  having  reached  its  full 
length,  the  filaments  shorten  and  draw  the  anthers  down  into 
the  corolla  tube  again.  While  this  is  going  on  the  style  remains 
elongated,  and  the  upright  hairs  on  the  outer  face  of  the  cleft 
portion  of  the  style  catch  the  pollen  as  the  open  anthers  are 
dragged  downward.  The  great  mass  of  pollen  is  thus  left  on  the 


156  GROWTH   AND    WORK  OF  PLANTS 

outside  of  the  exposed  stigma.  The  two  parts  of  the  stigma 
now  open  outward  and  become  recurved,  thus  exposing  the  stig- 
matic  surface  which  is  on  the  inner  face.  The  pollen  being 
caught  on  the  hairs  of  the  outer  surface  of  the  lobes  of  the  style 
cannot  come  in  contact  with  the  inner  stigmatic  face.  Now  that 
the  parts  of  the  stigma  become  recurved  and  the  stigmatic  sur- 
faces exposed,  the  pollen  from  certain  flowers  is  brushed  onto 
the  stigmatic  surfaces  of  others  by  insects  which  crawl  in  great 
numbers  over  the  disk  flowers,  and  thus  cross-pollination  is 
brought  about.  The  style  in  the  course  of  12  to  24  hours  then 
contracts  and  is  drawn  down  again  into  the  corolla  tube.  This 
took  place  in  the  cases  which  I  have  observed  during  the  late 
afternoon  and  evening.  In  the  cases  observed  by  myself  the 
anthers  are  drawn  into  the  corolla  tube  at  an  earlier  time  during 
the  previous  evening  and  night.  Some  movement  takes  place 
during  the  day  also,  and  some  flowers  lag  behind,  so  that  the 
process  is  going  on  continually,  but  the  greater  amount  of  change 
appears  to  go  on  during  late  afternoon,  during  the  night,  and 
in  the  early  morning. 

259.  Ray   flowers. — The    ray    flowers    have    a   rudimentary 
ovary  with  which  the  calyx  is  consolidated,  but  the  pistil  is  other- 
wise undeveloped  and  stamens  are  wanting.     Such  flowers  are 
sterile,  and  are  often  called  neuters.     The   corolla,  however,  is 
very  conspicuous.     The  petals  are  united  by  their  edges  in  such 
a  way  as  to  form  a  long,  broad,  leaf-like  organ,  except  at  the 
base  where  they  form  a  short  tube.     The  ray   flowers  of  the 
sunflower  do  not  show  wrell  the  number  of  divisions  of  the  corolla. 
But  the  ray  flowers  of  some  other  composites  do,  as  in  the  core- 
opsis, etc.,  where  the  end  is  five-toothed.     In  many  composites 
the  ray  flowers  are  pistillate,  and  therefore  develop  seed  like  the 
disk  flowers,  as  in  the  ox-eye  daisy,  or  white  weed.     In  the  dan- 
delion, chicory,  etc.,  all  of  the  flowers  are  strap-shaped  (like  the 
ray  flowers)  and  are  fertile.    For  composites  of  economic  impor- 
tance see  Chapter  XXXVI. 

260.  The  composite  flower  shows  the  highest  degree  of  spe- 
cialization, by  the  union  of  parts  and  the  massing  of  the  flowers, 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS        157 

of  all  the  seed  plants.  They  are  thus  believed  to  represent  the 
highest  stage  of  evolution  in  plants.  The  buttercup  flower  is 
much  more  simple  in  its  structure,  for  all  the  parts  are  separate 
and  distinct,  and  some  of  them  formed  in  large  numbers.  There 
are  other  dicotyledons,  however,  in  which  the  flowers  are  still  more 
simple  in  structure.  Some  of  the  flowers  which  we  have  studied 
show  different  steps  in  the  consolidation  of  parts  of  the  flower. 
In  the  evening  primrose  the  sepals  are  united  among  themselves 
(gamosepalous),  and  are  adnate  with  the  ovary,  while  the  petals 
and  stamens  are  seated  on  the  calyx  tube  instead  of  on  the  recep- 
tacle of  the  flower.  In  the  "  butter  and  eggs,"  not  only  is  the 
calyx  formed  by  the  united  sepals,  but  the  corolla  is  formed  by 
the  united  petals  (gamosepalous).  In  the  morning  glory,  calyx, 
corolla,  and  pistils  all  show  a  union  of  their  parts,  i.e.,  the  calyx 
is  gamosepalous,  the  corolla  is  gamopetalous,  and  the  pistil  is 
compound.  But  they  are  all  free,  except  the  stamens,  which  are 
inserted  on  the  inside  of  the  corolla.  In  the  composites  the 
calyx  tube,  formed  by  the  union  of  the  sepals,  is  consolidated 
with  the  outer  wall  of  the  ovary,  while  the  calyx  limb  or  free  part 
is  reduced  to  mere  scales  or  hairs,  or  is  inconspicuous.  The 
corolla  tube,  or  "  ray,"  formed  by  the  union  of  the  petals,  is 
seated  on  the  edge  of  the  calyx  tube.  The  stamens,  united  by 
their  anthers,  are  joined  to  the  inside  of  the  corolla  tube.  The 
pistil  is  compound  as  shown  by  the  divided  style,  but  there  is  a 
single  cavity  with  one  ovule  which  develops  into  a  seed.  The 
walls  of  the  ovule  (seed  coats)  are  consolidated  with  the  ovary, 
thus  forming  a  one-seed  fruit  known  as  an  akene. 


CHAPTER    XVII. 


FLOWERS,    THEIR   STRUCTURE    AND    KINDS    (Concluded). 
II.    FLOWERS    OF    MONOCOTYLEDON OUS    PLANTS. 

The  Indian  Corn. 
(Zea  Mays.) 

261.  The  Indian  corn  (or  "  maize," 
as  it  is  sometimes  called)  is  a  good 
illustration  of  a  plant  with  two  kinds 
of    flowers    (fig.    77),  the    staminate 
flowers,   those    having    stamens    but 
no  pistils;  and  the  pistillate  flowers, 
those  having  pistils  but  no  stamens. 
Such  flowers  are  really  of  two  forms 
(dimorphic).     Where  they  both  occur 
on  a  single  plant,  as   in  the  case  of 
the  Indian  corn,  the  plant  is  said  to 
be  dioecious,  i.e.,  of  two  "  households." 
362.  The  staminate  inflores- 
cence   of    Indian    corn. — This   is 
composed  of   several   spikes   in   the 
form  of  a  panicle   terminating   the 
shoot,  the  spike  which  forms  the  axis 
of  the  panicle  bearing  several  bran- 
ches, all  forming  what  is  commonly 
known  as  the  "  tassel"  of  the  corn. 
The  spikes  are  made  up  of  numerous 
spikelets  which  are  on  short  and  slender  branches  that  arise  from 
each  joint  of  the  axis  of  the  spike.     At  each  joint  there  are  usually 
two  spikelets  (sometimes  one  or  three),  one  nearly  or  quite  sessile 
and  the  other  on  a  short  stalk. 

158 


Fig.  1 1 6. 

Part  of  staminate  inflorescence  of 
Indian  corn. 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS        159 


263.  The  staminate  flowers  of  Indian  corn. — Each  spike- 
let  is  made  up  of  two  flowers,  one  bearing  perfect  stamens,  and 
another,  usually  sterile,  bearing  imperfect  stamens,  or  none.     The 
two  flowers  in  the  spikelet  are  enclosed  by  two  small  boot-shaped, 
ribbed  and    partially 

green  bracts,  known  as 

empty  glumes,  one   for 

each  flower.     If  we  dis- 

sect     the    flower   by 

spreading  these   empty 

glumes  apart,  and  with 

needles  loosen  from  the 

inside  the  other  parts  of 

the    flowers,    we     shall 

find  that  in  the   flower 

with    perfect    stamens, 

for    example,    there    is 

another    membranous 

bract    which   lies    next 

the    empty  glume    and 

often  fits  closely  within  it.     This  is  the  flowering  glume,  so  called 

because  it  lies  next  the  stamens.    Upon  the  other  side  of  the 

stamens  is  another  membranous  bract,  the  palea. 

264.  The  stamens  are  three  in  number,  which  is  the  rule  in 
the  grasses  and  cereals.     The  filaments  are  long  and  slender. 
The  anthers  are  two-loculed,  being  separate  at  each  end  and  con- 
nected by  the  tissue  of  the  "  connective"  for  the  greater  part  of 
their  length.     The  filament  is  attached  to  the  side  of  one  end  of 
this  connective.     Each  locule  of  the  anther  is  grooved  on  its 
outer  face,  so  that  it  appears  to  be  made  up  of  two  lobes,  but 
there  is  really  only  one.     At  the  time  of  flowering  the  filaments 
elongate  and  lift  the  anthers  far  out  of  the  flower.     The  fila- 
ments being  slender  and  delicate  are  bent  over  by  the  weight  of 
the  anther,  which  dangles  here  and  is  easily  agitated  by  the  wind. 
The  anther  sacs  open  on  the  outer  side  of  the  free  end.     A  split 
occurs  in  the  wall  along  the  groove  for  a  short  distance  and  the 


Fig.  117. 
Open  staminate  flowers  of  Indian  corn. 


160  GROWTH   AND    WORK   OF   PLANTS 

walls  bend  backward  so  that  a  nearly  circular  pore  is  formed. 
The  pollen  grains  are  nearly  spherical,  smooth,  and  quite  firm. 
As  the  anther  dangles  at  the  end  of  the  filament,  a  slight  jar, 
which  even  a  slight  breeze  would  give  it,  sets  the  pollen  grains 
rolling  out  of  the  opening.  They  usually  fall  out  in  large  num- 
bers. They  may  fall  directly  on  the  silk  of  the  ear  of  the  same 
stalk,  or,  as  is  more  often  the  case,  the  wind  carries  them  to  the 
silk  of  adjacent  plants.  The  Wades  of  corn,  and  the  ground  of 
a  field,  are  often  literally  covered  with  pollen  grains,  so  great  is 
the  number. 

265.  The  sterile  flower. — The  sterile  flower,  the  one  with 
imperfect  or  no  stamens,  lies  between  the  palea  of  the  fertile 
flower  and  the  other  large  empty  glume  which  covers  the  sterile 
flower.     If  care  is  used  in  dissecting  the  sterile  flower  by  spread- 
ing it  apart,  two  membranous  bracts  will  be  found.     They  are 
somewhat    shorter    and    narrower    than    the    others.     The    one 
lying  next  the  empty  glume  is  the  flowering  glume,  while  the 
other  is  the  palea,  and  it  lies  next  the  palea  of  the  fertile  flower. 
Between  these  two  membranous  bracts,  i.e.,  between  the  palea 
and  flowering  glume  of  the  sterile  flower,  may  often  be  found 
remnants  of  the  stamens,  sometimes  rudiments  only  in  the  form 
of  slender  threads,  two  or  three  of  them.     At  other  times  fila- 
ments and  anthers  are  both  formed,  but  the  pollen  is  unformed 
and  imperfect.     In  many  such  cases  the  filament  does  not  elon- 
gate and  the  anthers  do  not  emerge  from  the  closed  flower.     In 
a  few  cases  the  stamens  are  perfect  and  well  formed.     Such  a 
spikelet  contains  two  fertile  flowers. 

266.  The  pistillate  inflorescence  of  Indian  corn. — This  is 
formed  by  a  consolidation  of  several  spikes  into  one  body,  known 
as  the  "  ear"  of  corn  (fig.  118).     The  cob  is  formed  by  the  consoli- 
dation of  the  spikes,  the  flowers  being  borne  in  double  rows  alofig 
the  outer  surface,  so  that  there  is  always  an  even  number  of  rows 
of  grains  on  an  ear.     The  ears  arise  as  branches  at  some  of  the 
middle  joints  of  the  stem  in  the  axils  of  the  leaves.     When  young 
they  are  covered  by  the  leaf  sheath,  but  at  flowering  time  the  end 
appears  above  the  sheath  and  projects  for  some  distance.     The 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS        161 

ear  is  surrounded  and  covered  by  a  large  number  of  leafy  bracts, 
called  "  husks."     They  are  in  reality  leaves;  the.  outer  ones  are 


Fig.  118. 
Pistillate  inflorescence  of  Indian  corn,  showing  long  styles,  the  "  silk." 

green,  and  often  the  tip  terminates  in  a  true  blade,  so  that  the 
husk  part  may  correspond  to  the  leaf  sheath.     At  the  time  of 


1 62 


GROWTH   AND    WORK   OF   PLANTS 


flowering  the  tuft  of  silk  emerges  from  between  the  husks  at  the 
end  of  the  ear. 

267.  The  pistillate  flowers  of  Indian  corn. — The  pistillate 
flowers  are  well  seen  by  taking  a  young  ear  of  corn  soon  after  the 
silk  has  emerged.  If  the  husks  are  carefully  stripped  off  with- 
out breaking  the  silk,  and  this  is  shaken  out  so  as  to  separate  the 
threads  as  much  as  possible,  it  will  be  seen  that  each  long  thread 
of  silk  is  connected  with  the  tip  of  a  small  and  young  grain  of 
corn.  This  is  the  pistil  of  the  flower.  The  thread  of  silk  is  the 
style  and  the  young  grain  of  corn  is  the  ovary.  If  the  surface  of 
the  silky  threads  is  examined  with  a  hand  lens  for  some  distance 
over  the  portion  which  extends  outside  of  the  husks,  numerous 
short  hairs  will  be  seen.  These  serve  to  hold  the  pollen  grains. 
It  is  easy  to  see  that  when  the  pollen  grain  germinates  the  tube 
must  travel  a  long  distance  to  reach  the  egg  cell  in  the  ovule. 


Fig.  119. 
Spikelet  of  oat. 
showing 
glumes. 


Fig.  120. 

One      glume      re- 
two    moved,   showing    fer- 
tile  flower. 


Fig.  121. 

Flower  opened, 
snowing  two  palets, 
three  stamens,  and 
two  lodicules  at  base 
of  pistil. 


Fig.  122. 
Section    showir 
ground    plan    < 
lower,   a,  axis. 


268.  There  is  a  cluster  of  delicate  white  membranous  scales 
which  envelop  each  ovary  at  this  stage,  so  that  only  the  tip  of 
the  ovary,  where  the  style  is  attached,  is  exposed.  In  the  ripe 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS        163 


ear  of  corn  these  form  the  chaff,  which  mostly  remains  on  the  cob 
when  the  corn  is  shelled.  This  cluster  of  chaff  with  the  pistil 
corresponds  to  the  spikelet,  and  in  fact  is  a  spikelet  with  two 
flowers,  one  fertile  and  one  sterile,  the  sterile  one  lying  below 
the  fertile  one.  It  is  not  a  very  easy  matter  to 
dissect  out  these  parts  to  determine  them,  since 
they  are  soft,  delicate,  and  some  of  them  much 
plaited  and  folded.  But  in  flowers  where  the 
grains  are  about  one-fifth  grown  they  can  be  teased 
out  so  that  one  can  make  out  the  membranous 
bracts.  Here  it  will  be  seen  that  the  two  outer- 
most ones  are  the  empty  glumes  of  the  two  flowers. 
Between  one  of  the  empty  glumes  and  the  grain 
of  corn  is  the  flowering  glume,  and  the  palea  of 
this  fertile  flower  is  on  the  other  side  of  the  grain 
of  corn.  The  two  scales  between  this  and  the 
empty  glume  of  the  sterile  flower  are  the  palea 
and  flowering  glume  of  the  sterile  flower  (compare  Flg-  I23- 

Flower    of    oat, 

Oat  flowers,  figS.   IIO  tO   123).  showing  the  upper 

palet    behind    and 

269.  The  corn  is  a  representative   of  the  the  two  lodkuies 

in  front. 

Monocotyledons  making  up  the  great  family  of 
grasses  (Gramineae),  including  many  valuable  economic  plants  as 
the  grasses,  cereals,  sorghum,  sugar  cane,  etc.     For  this  study  see 
Chapter  XXXVI. 

Jack-in-the- Pulpit,  Indian  Turnip. 
(Arisczma  triphyllum.} 

270.  The  Indian  turnip  inhabits  moist,  shady  woods  or  groves, 
and   flowers  from  April  to    June.     Its  underground  perennial 
stem  is  a  corm  (paragraph  74)  which  is  very  acrid  to  the  taste.  The 
annual  flowering  shoot  is  formed  in  the  bud  at  the  apex  of  the  corm 
during  autumn  and  winter.     The  plants  are  about  30  cm.  (i  foot) 
high.     The  leaves  are  divided  into  three  leaflets.     The  flower 
shoot  is  very  odd  and  interesting.     It  is  in  the  form  of  a  spadix, 
a  cylindrical  structure,  the  free  end  sterile  and  with  the  small 
imperfect  (either  staminate  or  pistillate)  flowers  crowded  around 


164 


GROWTH   AND    WORK   OF   PLANTS 


the  lower  part.  The  spadix  is  enclosed  in  a  leaf-like  structure, 
forming  a  broad  cylindrical  tube  (the  "  pulpit  ")  below,  and  above 
tapering  into  a  strap-shaped  part  (spathe)  which  bends  forward 

over  the  pulpit.     In  some  plants  the 

!staminate  and  pistillate  flowers  are  borne 
on  the  same  spadix  (plants  monoecious), 
but  usually  they  are  all  of  one  kind  on  a 
spadix  (plants  dioecious). 
271.   A  little  observation  will  show 
that  the  pistillate  plants  are  the  larger 
and  have  larger  corms,  while  the  stam- 
inate  plants  are  smaller.     The  larger 
corms  have  more  stored  food  and  thus 
produce  a  larger  aerial  shoot.    But  why 
they  should  produce  pistillate  flowers 
is    not    so  clear,  though    it  probably 
has   some  connection  with  the  abun- 
dant food  supply.     It  is  evident,  how- 
ever, that  this  is  a  useful  distribution 
of  the  flowers,  since  the  pistillate  flowers 
produce  the  seed,  which  makes  a  greater 
drain  of  food  from  the  corm  than  the 
mere  production  of  stamens  and  pollen 
would.     Seed  formation  of  the  smaller 
pistillate  plants  sometimes  makes  such 
a   drain  of   food   from   their   smaller 
corm,    that   the    ensuing    year    they 
change  to  staminate  plants.      In  fact 
the  change  from  pistillate  to  staminate 
plants  can    be    demonstrated    experi- 
mentally, by  removing  the  larger  part 
of  the  corm  with  a  knife  during  late 
summer  or  early  autumn,  before  the  nature  of  the  flowers  for 
the  coming  year  has  been  fixed.     It  follows  from  all  these  facts 
that  seedlings,  or  offsets  from  the  corm,  when  they  flower  for  the 
first  time  probably  bear  staminate  flowers.     In  a  few  years,  if 


Fig.  124. 

Jack-in-the- pulpit  or  Indian 
turnip  (Arisaema  triphyllum), 
spathe  removed,  showing 
spadix;  the  two  upper  figures 
with  pistillate  flowers,  lower 
figures  with  staminate  flowers. 


FLOWERS,    THEIR   STRUCTURE   AND    KINDS        165 


they  are  favorably  situated  so  that  the  corm  attains  a  suitable 
size,  they  then  bear  pistillate  flowers. 

272.  The  Jack-in- the-pulpit  belongs  to  the  arum  family. 
A  number  of  the  species  are  grown  in  greenhouses  for  the  orna- 
mental foliage,  while  in  some 
others  the  spathe  is  brightly 
colored,  as  in  the  calla  lily 
(Richardia),  which  is  not  a 
true  lily.  Another  very  in- 
teresting member  of  this 
family  is  the  skunk  cabbage, 
so  called  because  of  its  pecul- 
iar odor  and  large  cabbage- 
like  leaves.  Both  kinds  of 
flowers  are  borne  on  the 
same  spadix,  which  is  club- 
shaped. 


Gladiolus. 


Fig.  125. 
A  group  of  jacks. 


273.  The  showy  flowers 

of  gladiolus  arise  in  two  ranks  on  a  long  terminal  shoot,  but 
they  bend  to  one  side,  giving  the  appearance  of  a  long  unilateral 
spike,  which  sometimes  has  a  slight  tendency  to  a  spiral  form. 
The  base  of  the  flower  is  covered  by  two  leaf-like  bracts.  The 
showy  part  of  the  flower  is  the  perianth,  but,  unlike  the  lily,  the 
six  parts  of  the  perianth  are  united  toward  the  base  into  a  tube, 
which  is  attached  to  the  upper  part  of  the  ovary,  and  the  lower 
part  of  the  tube  is  coalesced  with  the  outer  part  of  the  ovary. 
The  parts  of  the  perianth  are  somewhat  irregular,  so  that  it 
has  in  some  varieties  a  decidedly  two-lipped  appearance.  The 
upper  petal  (upper  lip)  is  usually  covered  by  the  two  lateral 
sepals,  while  the  two  lower  petals  are  covered  by  the  lower  sepal 
and  the  two  lateral  ones. 

274.  The   stamens. — There   are   three   stamens.     These   are 
seated  on  the  upper  part  of  the  tube  of  the  perianth,  on  the  middle 


1 66 


GROWTH   AND    WORK   OF   PLANTS 


line  of  what  would  correspond  to  the  sepals,  or  outer  members 
of  the  perianth.  The  filaments  are  long  and  attached  by  a  joint 
near  one  end  of  the  anther.  The  anthers  are  long  and  two-loculed. 
275.  The  pistil  is  compound  and  consists  of  three  parts,  as  can 
be  seen  by  the  three  lobes  of  the  stigma.  The  style  is  long,  slender, 
rises  along  the  inner  face  of  the  upper  lip,  and  the  stigmas  lie  just 


Fig.  126. 

Flowers  of  Glad.olus:  at  right, 
irtly  dissected.     The  six  petal- 
ike  parts  form  the  "perianth." 

underneath  the  apex  of  the  upper  member  of  the  perianth,  with 
the  three  anthers  directly  in  front  of  the  stigmas  or  slightly  below 
them.  The  ovary  is  elongate,  three-angled,  and  with  three  locules. 

276.  The  gladiolus  belongs  to  the  order  of  lilies  (Liliales), 
which  includes  many  plants  with  beautiful  flowers,  cultivated  for 
ornamental  purposes,  as  tulips,  crocuses,  daffodils  (Narcissus), 
hyacinths,   iris,   lilies,   etc.      The  cultivation  of  the   Easter  lily 
(Lilium  harrisii  and  L.  longiflorum)  forms  a  large  industry  in 
Bermuda  and  Japan,  from  whence  come  most  of  the  bulbs,  which 
are  forced  in  greenhouses  by  the  florists.     Some  plants  in  this 
order  are  used  for  food,  as  asparagus,  onion,  etc. 

277.  The  orchid  family  (Orchidaceae),  also  belonging  to  the 
Monocotyledons,  contains  many  plants  with  beautiful  flowers  and 
wonderful  mechanisms  for  cross-pollination  by  the  aid  of  insects.* 

*  See  Darwin,  On  the  fertilization  of  orchids  by  insects. 


CHAPTER    XVIII. 
METHODS   OF    POLLINATION. 

278.  The  necessity  of  pollination. — Pollination  is  the  trans- 
ference of  the  pollen  from  the  anthers  to  the  stigma  of  the  pistil. 
This  is  necessary  in  order  that  the  pollen  grain  may  germinate, 


Fig.  127. 
Photomicrograph  of  pollen  grains  of  sunflower,  highly  magnified. 

and  that  the  pollen  tube,  by  making  its  way  down  through  the 
style,  may  reach  and  enter  the  ovule,  to  carry  the  sperm  cell 
(the  fertilizing  element)  to  the  egg  cell.  The  union  of  the  sperm 
cell  and  egg  cell  brings  about  the  fertilization  of  the  egg  cell, 
which  is  necessary  (except  in  rare  cases)  in  order  that  the  egg 
may  develop  into  the  embryo  and  bring  about  the  formation  of 
the  seed.  There  are  many  different  devices,  or  mechanisms,  in 
the  flower  structure  for  bringing  about  pollination.* 
*  See  Darwin,  Cross  fertilization,  etc. 

167  v 


l68  GROWTH   AND    WORK   OF  PLANTS 

279.  The  pollen  grains  and  how  they  are  shed  from  the 
anther. — The  form  and  parts  of  the  stamen  have  been  described 
in  Chapters  XVI,  XVII.     The  anthers  open  in  different  ways  in 
different  flowers.     In  some  the  anther  opens  by  long  slits,  in  others 
by  a  trap  door,  and  in  others  by  a  pore  at  the  end  of  the  locule. 
The  pollen  grains  are  all  free,  and  loose  or  dusty,  or  they  may  be 
held  rather  loosely  together  by  a  viscid  or  fibrous  substance. 
In  some  flowers,  especially  the  orchids,  the  milkweeds,  etc.,  the 
pollen  grains  are  held  in  one,  or  several,  more  or  less  compact 
masses  called  a  pollinium. 

280.  Kinds  of  flowers  as  regards  methods  of  pollination. — 
Most  flowers  can  be  placed  in  three  different  groups  according 
to  the  general  method  of  pollination.     First.    Those  which  are 
self -pollinated,  where  the  anthers  lie  close  to  the  stigma,  or  above 
them,  and  open  at  the  same  time  that  the  stigmas  are  ready  to 
receive  the  pollen.     The  pollen  is  usually  shed  directly  on  the 
stigma  in  the  same  flower.     Second.    Where  the  pollen  is  trans- 
ported by  the  wind  to  the  stigmas  of  a  different  flower.     These 
are  wind- pollinated  flowers  (anemophilous  flowers).     Though  in 
many  cases   self-pollination  takes  place,  cross-pollination  is  the 
rule  because  of  certain  peculiarities  of  the  flower  (see  Darwin, 
Cross  fertilization,  etc.).     The  pollen  in  such  flowers  is  dusty,  so 
that  it  is  easily  wafted  by  the  wind.     Third.    When  the  pollen  is 
carried  by  insects  from  one  flower  to  another.     These  are  insect- 
pollinated    flowers    (entomophilous    flowers.     Self-pollination    in 
some  cases  may  take  place  here).     The  pollen  in  these  flowers  is 
usually  held  together  loosely  or  firmly  by  a  viscid   substance. 
Humming  birds  also  assist  in  the  pollination  of  some  flowers. 
In  a  state  of  cultivation,  especially  in  greenhouses,  it  is  some- 
times necessary  to  hand-pollinate  the  flowers  of  some  plants,  as 
tomatoes,  strawberries,  etc. 

281.  A  knowledge  of  these  laws  is  of  great  importance  to 
the  horticulturist  and  florist.     In  many  varieties  of  pears,  although 
the   flowers   are  perfect,   it  has  been  found  that  the  pollen  is 
impotent  or  very  weak,  not  only  on  the  pistil  of  the  same  flower 
and  the  flowers  of  the  same  tree,  but  in  all  the  flowers  of  that  par- 


METHODS  OF  POLLINATION  169 

ticular  variety.  If  an  orchard  of  this  variety  is  planted,  without 
the  admixture  of  a  different  variety  having  pollen  potent  for  the 
pistils  of  the  first  variety,  no  fruit  or  but  little  fruit  will  set.  But 
if  a  tree  of  another  variety  is  planted  here  and  there  through  the 
orchard,  with  trees  of  the  variety  from  which  fruit  is  desired,  and 
for  which  the  pollen  of  the  fertilizing  variety  is  potent,  abundant 
and  fine  fruit  will  form.*  This  impotency  of  the  pollen  of  one 
variety  for  all  of  the  flowers  of  the  same  variety  is  not  due  to  any 
deficiency  in  the  pollen  itself,  but  to  a  lack  of  affinity  between 
the  sperm  cell  in  the  pollen  tube  and  the  egg  cell  in  the  ovule. 
Varieties  which  are  perfectly  sterile  (i.e.,  unadapted  or  unfitted) 
to  pollen  of  their  own  flowers  may  be  abundantly  fertile  (adapted 
or  fitted)  in  cross-pollination.  Rainy  weather  during  flowering 
time  interferes  with  cross-pollination,  since  it  prevents  the  visits 
of  bees. 

In  the  case  of  a  number  of  varieties  of  strawberries,  it  is 
necessary  to  plant  a  "fertilizing"  variety  among  them  in  order 
to  insure  fertilization,  since  some  varieties  are  sterile  to  their  own 
pollen. 

282.  Close-pollination  and  cross-pollination. — Close  polli- 
nation   is   the    same    as    self-pollination,    where    the    stigma    is 
pollinated  with  pollen  from  anthers  of  the  same  flower.     Cross- 
pollination  occurs  when  the  pollen  is  transferred  from  the  anthers 
of  one  flower  to  the  stigmas  of  another  flower  either  near  or  re- 
mote.    Cross-pollination  takes  place  through  the  agency  of  the 
wind,  insects,  birds,  or  by  the  hand  of  man. 

CLOSE    POLLINATION. 

283.  Close  pollination  can  take  place  in  a  great  many 
different  flowers  where  cross-pollination  also  takes  place.     It  is 
remarkable  that  in  many  of  these  cases  the  pollen  from  a  different 
flower  or  plant  is  often  more  "  potent"  than  the  pollen  from  the 
same  flower.     In  these  flowers,  where  close  pollination  alone  takes 

*  See  "The  Pollination  of  Pear  Flowers,"  U.  S.  Dept  Agr.  Bull.  No.  5, 
Div.  Veg.  Path.,  1894. 


i  yo 


GROWTH   AND    WORK   OF   PLANTS 


place,  there  may  be  little  or  no  seed  or  fruit  developed,  but  when 

cross-pollination  takes 
place  an  abundance 
of  seed  is  formed. 
Even  when  pollen  from 
the  same  and  from  a 
different  flower  is  de- 
posited on  the  stigma, 
the  pollen  from  the  dif- 
ferent flower  prevails. 
Cross-pollination  is  im- 
portant for  the  plant, 
since  it  insures  greater 
vigor  and  greater  plas- 
ticity in  the  offspring, 
survive  in 


Fig.  128. 
The  pendent  flower  of  Y.ucca.  showing  position  of  sta- 


mens and  the  ribbed  ovary.  —  After  Riley  and  Trelease. 

which   make    it    better   fitted   to 
the   struggle   for  existence.      Still   there    are 
flowers  in  which  the  usual   method  of   pol- 
lination is  a  close  pollination. 

284:.  Cleistogamous  flowers.  —  Close  pol- 
lination always  takes  place  in  cleistogamous 
flowers,  of  course  if  left  to  themselves.  Cleis-  c 
togamous  flowers  are  those  which  remain 
closed  during  the  process  of  pollination  and 
fertilization.  The  violet  is  an  excellent  ex- 
ample. The  showy  flowrers  which  are  so 
conspicuous  rarely  develop  seed.  The  greater 
quantity  of  seed  is  formed  in  flowers  which 
are  not  showy  and  which  are  covered  by 
the  soil  or  leaf  mold.  They  remain  closed, 
and  the  pollen  from  the  stamens  is  shed 
on  the  stigma  of  the  same  flower. 

285.  Pollination  of   the  yucca  by  the 
moth  Pronuba.—  This  is  a  remarkable  case 


Fig.  129. 


and  Trelease- 


of    close    pollination    brought    about    by    an 

insect.     The  pollen  is  somewhat  sticky  and  without  some   aid 


METHODS  OF  POLLINATION 


171 


could   not    be    deposited   in   the    funnel-shaped    stigma.      The 
moth   resting    quietly  in  the    flower  during  the    day,   at  dusk 

crowds  down  over 

the  stamens,  digs 

out   some   of   the 

pollen  mass  with 

her    foot,    passes 

down  on  the  ovary 

over   one   of    the 

furrows  directly 

over  where    the 

ovules  are  located, 
The  position  of  p™WM&a  pierces  the  ovary 

on  the  stamen  of    Yucca  „  'XL, 
With 


B 


when  collecting  pollen  and 


^^r^c, 
OVlpOSl- 


Fig.  131. 

A  mature  capsule  of  Yucca,  showing 
perforations  made  by  larvae  of  Pro- 
nuba  in  escaping.  —  After  Riley  and 


when  thrusting  it  into  the  ,  i    _.10  _..«.<,  0_ 

stigmatic  funnel.  —  After  tor  and  plants  an 
egg  in  an  ovule. 

Then  she  passes  on  to  the  end  of 
the  pistil  and  crowds  the  pollen 
into  the  funnel-shaped  opening  of 
the  stigma.  She  repeats  this  proc- 
ess several  times,  depositing  sev- 
eral eggs  and  placing  an  abundance  Trelease- 
of  pollen  in  the  stigma,  which  insures  the  development  of  a  large 
number  of  seeds,  some  of  which  can  be  used  for  food  by  the 
young  larvae. 

CROSS-POLLINATION  BY  THE  WIND. 

286.  While  wind  pollination  takes  place  in  quite  a  variety 
of  plants,  it  is  the  chief  method  among  the  grasses,  cereals,  Indian 
corn,  the  amentiferous  trees  and  shrubs  (those  bearing  catkins), 
and  among  the  conifers.  Whoever  has  been  in  a  cornfield  at  the 
time  of  pollination  will  realize  this.  In  the  pines  among  the 
conifers,  the  pistillate  cone  stands  erect  and  the  scales  flare  out- 
ward during  pollination.  The  pollen  is  caught  on  these  scales 
and  rolls  down  to  the  lower  end,  where  it  is  caught  in  a  viscid 
substance  in  the  micropyle  of  the  ovule. 


GROWTH  AND    WORK   OF  PLANTS 

CROSS-POLLINATION  BY  INSECTS. 
287.  How  insects  are  attracted  to  flowers.— In  order  to 
secure  cross-pollination  through  the  aid  of  insects,  the  insects 
must  be  lured  or  attracted  to  the  flowers  for  some  highly  prized 
food.  Provision  of  food  is  made  in  the  nectar  which  is  developed 
in  special  nectar  glands,  or  nectaries,  in  these  flowers.  The  odor 
from  flowers  probably  has  more  influence  in  attracting  insects  to 
them  than  anything  else.  This  is  very  striking  in  the  case  of 
night-blooming  flowers,  which  usually  have  strong  fragrant  odors 
and  attract  the  moths  which  fly  at  night.  In  addition  most 
flowers  adapted  for  cross-pollination  by  insects  have  showy  parts, 
which  by  their  size  and  color  attract  the  insects,  and  stand  for 
them  as  a  sign  of  those  flowers  which  produce  nectar.  In  the 
larger  number  of  cases  the  petals  are  the  showy  parts  of  the  flower. 
Sometimes  it  is  the  sepals,  especially  in  the  apetalous  flowers, 
as  in  the  marsh  marigold,  etc.  In  other  cases  the  bracts  of  the 
flowers  are  colored  and  showy,  as  in  the  flowering  dogwood.  In 
many  composite  flowers  it  is  the  ray  flowers  which  are  showy 
and  serve  to  attract  the  insects.  In  many  cases  these  ray  flowers 
are  neutral,  or  do  not  develop  seed,  so  that  their  sole  function  is 
to  attract  insects,  while  the  inconspicuous  disk  flowers  provide 
the  nectar  and  produce  the  seeds.  The  neutral  showy  flowers 
in  the  cranberry  tree  or  wild  guelder  rose  (Viburnum  opulus)  are 
exterior  to  the  perfect  inconspicuous  flowers.  This  massing  of 
flowers  into  flower  clusters,  heads,  etc.,  is  of  great  advantage 
since  the  flowers  are  made  more  conspicuous,  the  odors  are  more 
centralized,  and,  as  in  the  heads  of  composites,  the  insects  crawl- 
ing over  the  head  cross-pollinate  rapidly  a  great  many  flowers. 
According  to  Lubbock,  flies  are  mostly  attracted  to  the  flowers 
with  the  duller  colors,  as  brownish,  dark  purple,  dull  yellow,  or 
greenish  flowers.  Some  flowers  have  carrion  odors  which  also 
serve  to  attract  flies.  Butterflies  and  bees  are  attracted  by  the 
bright  colors,  as  red,  blue,  violet.  Experiments  seem  to  show 
that  insects  cannot  see  the  form  of  objects  distinctly  at  distances 
greater  than  four  to  six  feet,  but  the  colors  of  objects  can  be  seen 
at  a  greater  distance. 


METHODS  OF  POLLINATION  173 

288.  Landing  places  for  insects. — Many  of  the  flowers  which 
attract  insects  are  irregular  (those  with  bilateral  symmetry)  and 
some  portions  of  the  flower  are  especially  adapted  to  serve  as  a 
landing  place.  This  is  often  the  lower  lip  of  the  flower,  or  one 
or  more  of  the  lower  petals  (where  more  than  one  petal  they  are 


Fig.  132. 

Epi partis  with  portion  of  perianth  removed  to  show  details.  /,  labellum;  st,  stigma; 
r,  rostellum;  />,  pollinium.  When  the  insect  approaches  the  flower  its  head  strikes  the  disk 
of  the  pollinium  and  pulls  the  pollinium  out.  At  this  time  the  pollinium  stands  up  out  of  the 
way  of  the  stigma.  By  the  time  the  insect  moves  to  another  flower  the  pollinia  have  moved 
downward  so  that  they  are  in  position  to  strike  the  stigma  and  leave  the  pollen.  At  the  right 
is  the  head  of  a  bee,  with  two  pollinia  (a)  attached. 

often  consolidated).  The  keel  of  the  papilionaceous  flowers,  the 
lower  lip  of  bilabiate  flowers,  the  lower  petal  of  the  canna  flower, 
and  the  labellum  of  the  orchids,  are  examples.  In  the  violet  the 
insect  rests  on  the  two  lower  petals  while  extracting  the  nectar 
from  the  nectary  in  the  spur. 

289.  Honey   guides. — Some  flowers   have   "  honey  guides," 
bright-colored  lines  on  the  petals  facing  the  insect  as  it  alights, 
which  lead  down  to  the  nectary. 

290.  Flower   structures   suited   to   the  visits   of   special 
insects. — Flowers  with  long  spurs,  which  are  formed  from  the 
prolongation  of  one  or  more  sepals  or  petals  into  a  tube,  prevent 
most  insects,  except  those  with  a  long  proboscis  or  sucking  tube, 
from  obtaining  nectar.    The  sphinx  moths  and  humming  birds  are 
visitors  to  many  of  these  flowers.     Examples  are  seen  in  the 
columbine,  nasturtium,  etc.     The  outer  parts  of  some  flowers 


GROWTH   AND    WORK   OF  PLANTS 

are  covered  with  a  sticky  substance,  which  probably  prevents 
crawling  insects  like  ants,  which  could  not  aid  in  cross-pollination, 
from  reaching  the  nectar.  This  is  shown  in  the  catchflies  (Silene), 
where  the  peduncle  of  the  flower  is  sticky;  in  the  mullein,  where 
the  hairs  on  the  calyx  are  sticky;  and  in  the  rhododendrons,  where 
the  calyx  and  corolla  are  sticky.  In  many  flowers  of  the  pea 
family  the  stamens  are  protected  in  the  keel  formed  of  the  two 
lower  petals.  Many  flowers,  as  the  dandelion,  hawkweed,  chic- 
ory, pond  lily,  crocus,  close  on  cloudy  and  rainy  days  and  thus 
are  protected  from  rain.  As  stated  above,  self  or  close  pollination 
is  prevented  in  many  flowers:  first,  in  imperfect  flowers  (monoe- 
cious and  dioecious  flowers);  second,  flowers  in  which  the  stamens 
and  pistils  are  of  different  lengths;  third,  flowers  in  which  the 
stamens  and  pistils  open  at  different  times;  fourth,  the  special 
and  peculiar  structures  found  in  many  orchids,  in  the  canna,  etc., 
where  movements  of  certain  of  the  floral  organs,  in  connection 
with  insect  visits,  assist  in  cross-pollination,  or  the  insect  is  led 
into  one  part  of  the  flower  and  out  at  the  other  in  such  a  way  as 
to  bring  about  cross-pollination. 

291.  Imperfect  flowers. — In  those  flowers  where  the  stamens 
and  pistils  are  in  different  flowers,  often  in  different  flower  clusters 
or  on  different  plants,  cross-pollination  is  necessitated.      Many 
of  these  are  wind-pollinated  as  stated  above  in  many  of  the  trees 
with  catkins.     Others  of  this  group  are  insect-pollinated,  as  in 
the  willow  and  chestnut.     Here  the  stamens  and  pistils  are  the 
showy  parts,  and  the  nectar  also  attracts  the  insects. 

292.  Flowers  with  stamens  and  pistils  of  unequal  length. 
— In  flowers  where  the  stamens  and  pistils  are  of  unequal  length, 
so  that  when  the  insect  visits  one  flower  one   part  of  its  body 
comes  in  contact  with  the  pistil  and  another  part  comes  in  contact 
with  the  anthers,  this  part  brushes  off  and  carries  some  of  the 
pollen.     In  the  next  flower,  or  one  of  the  succeeding  ones  which 
the  insect  visits,  the    length  and   position  of  the    stamens  and 
pistils  will  be  reversed,  so  that  the  pollen  from  one  of  the  pre- 
viously visited  flowers  will  be  brought  in  contact  with  the  stigma 
and  its  viscid  surface  will  pull  off  some  of  the  pollen.     The  common 


METHODS  OF  POLLINATION 

bluet  (Housionia)  and  the  bell  flower  (Campanula)  are  examples, 
as  well  as  the  primrose  so  commonly  grown  in  greenhouses.  This 
plant  can  be  used  for  study  and  demonstration.  Not  only  do 
the  length  and  position  of  the  stamens  and  pistils  in  such  flowers 


Fig.  133- 
Dichogamous  flowers  of  Primula. 

favor  cross-pollination  by  insects,  but  Darwin  has  shown  that  in 
some  of  them  the  pollen  of  the  long  stamens  is  impotent  or  weak 
on  the  short  pistil  of  the  same  flower,  but  is  prepotent  on  the 
long  pistil  of  another  flower,  and  so  the  pollen  of  the  short  stamens 
is  prepotent  on  the  short  pistil  of  a  different  flower. 

293.  Flowers  in  which  the  stamens  mature  first. — This 
is  shown  in  the  great  willow  herb  or  fire  weed  (Epilobium).  When 
the  stamens  are  mature  the  four  stigmas  are  closed  and  the  style 
is  bent  backward.  Later  when  the  anthers  have  shed  their  pollen, 
the  style  straightens  out,  and  the  stigmas  open  and  become  recep- 
tive. In  the  evening  primrose  (CEnothera  biennis  =  Onagra 
biennis)  the  stamens  also  mature  first  (see  paragraph  237).  The 
same  is  true  of  the  high  mallow  with  purple  flowers.  The  sta- 
mens are  erect,  shed  their  pollen,  then  wither  and  become  recurved, 
while  the  styles  then  elongate  and  the  stigmas  become  receptive. 
In  most  of  the  composite  flowers  the  stamens  mature  first  (see 
the  study  of  the  sunflower,  paragraphs  254-258).  In  the  bell- 
flower  (Campanula)  the  stamens  are  joined  by  their  anthers  into 
a  tube,  and  mature  their  pollen  before  the  stigma,  which  is  inside 
the  tube,  is  receptive  and  open.  The  stigma  now  elongates,  and 


176  GROWTH   AND    WORK   OF   PLANTS 

the  brush  on  the  outside  of  the  closed  stigma  sweeps  out  the 
pollen.     The  stigma  now  opens,  the  lobes  curving  outward  so 


Fig.  134- 

Proterandry  in  the  bellflower  (Campanula).  Left  figure  shows  the  syngenoecious  stamens 
surrounding  the  immature  style  and  stigma.  Middle  figure  shows  the  immature  stigma  being 
pushed  through  the  tube  and  brushing  out  the  pollen;  while  in  the  right-hand  figure,  after 
the  pollen  has  disappeared,  the  lobes  of  the  stigma  open  out  to  receive  pollen  from  another 
flower. 

that  the  pollen  does  not  fall  on  its  upper  receptive  surface,  but  the 
visiting  insect  brings  pollen  from  another  flower. 

294:.  Flowers  in  which  the  pistils  mature  first. — In  the 
figwort  the  flower  is  urn-like,  and  the  mature  stigma  is  thrust  out- 
side of  the  flower  by  the  long  style,  while  the  stamens  are  curved 
backward  in  the  flower.  When  the  stigma  of  this  flower  is  past 
the  receptive  stage,  the  stamens  straighten  out  and  bring  the 
anthers  to  the  outside  of  the  flower,  where  they  shed  their  pollen 
so  that  a  visiting  insect  can  carry  it  to  another  flower  in  which 
the  stigma  is  receptive.  In  the  skunk  cabbage  the  stamens  in 
the  flowers  of  some  plants  mature  first,  while  in  other  plants  the 
pistils  mature  first. 

295.  Movements  executed  by  stamens  or  pistils  to  aid  in 
cross-pollination. — The  movements  of  the  pistils  and  stamens 
described  in  the  study  of  the  sunflower  (paragraph  258)  and  of 
the  bellflower  in  the  preceding  paragraphs  are  illustrations.  A 
remarkable  case  is  seen  in  the  mountain  laurel  (Kalmia).  The 
stamens  are  bent  outward  and  the  anthers  are  held  in  little  pockets 


METHODS  OF  POLLINATION 


1/7 


near  the  base  of  the  petals.  When  the  insect  is  crawling  over  the 
flower  and  touches  the  stamens,  the  anthers  are  released  suddenly, 
fly  up  and  throw  the  pollen  on  the  body  of  the  insect.  The  action 


Fig.  135. 

Kalmia  latifolia,  showing   position  of   anthers  before  insect  visits,  and  at   the   right  the 
scattering  of  the  pollen  when  disturbed  by  insects.     Middle  figure  section  of  flower. 

of  the  stamens  can  be  seen  by  touching  the  filaments  with  a  pencil 
or  other  object.  The  common  garden  sage  (Salvia)  presents  a  very 
peculiar  structure  and  move- 
ment of  the  stamens  (fig.  136). 
As  the  insect  enters  the  flower 
it  pushes  against  the  lower 
sterile  anther  lobe,  which 
causes  the  connective  to  swing 


st 


n 


Fig.  136. 


on  its   hinge  in  such  a  way 

as    to    bring    the    Upper    lobes        Two   flowers   of   common   sage,    one  of  them 
.  ...  ..          visited  by  a  bee.     After  Lubbock. 

ready  to  discharge  the  pollen 

down  on  the  back  of  the  insect.  On  visiting  another  flower 

where  the  pistil  is  older  the  in- 
sect on  entering  brushes  some 
of  the  pollen  off  on  to  the 
stigma.  The  orchids  show  some 
of  the  most  remarkable  move- 
ments of  any  flowers  during 
cross-pollination.  In  some  the 

pollen  mass  (pollinium)  is  attached  to  a  slender  curved  stalk  which 

is  held  in  tension  like  a  spring,  and  on  the  other  end  is  a  viscid 


Fig.  137- 
Flower  and  stamens  of  common  sage. 


GROWTH   AND    WORK   OF   PLANTS 

disk.  When  the  insect  alights  on  the  labellum  and  touches  a 
sensitive  structure,  the  pollinium  is  set  free,  the  tension  of  the 
curved  stalk  causes  it  to  fly  out  like  a  spring,  and  the  viscid 
disk  attaches  itself  to  the  head  or  to  the  proboscis  of  the 
insect.  In  this  position  it  stands  pointing  upward,  holding  the 
pollinium  too  high  to  touch  the  stigmatic  surface  of  that  flower. 
In  the  course  of  half  a  minute  or  a  minute,  the  stalk  curves  down- 
ward in  such  a  position  that  the  pollinium  will  strike  the  stig- 
matic surface.  But  by  this  time  the  insect  has  gone  to  another 
flowrer  and  cross-pollination  is  effected.*  In  members  of  the  pea 
family  (plants  like  Cytisus,  Spartium,  etc.,  grown  in  greenhouses 
are  excellent  to  experiment  with)  the  pistils  and  stamens  are  held 
in  the  keel.  When  an  insect  alights  on  the  keel  the  style  suddenly 
flies  upward  and  the  brush  of  hairs  throws  out  the  pollen  on  to 
the  body  of  the  insect.  When  it  visits  another  flower  in  which 
the  stigma  shows  above  the  keel  and  is  receptive,  some  of  the  pollen 
is  brushed  on  to  the  stigma.  In  the  canna  flower  the  pollen  is 
shed  from  the  anther  (while  the  flower  is  still  closed)  and  glued 
on  to  one  side  of  the  broad  style  right  by  the  side  of  the  stigmatic 
surface  but  not  on  it.  As  the  flower  partly  opens,  bumblebees 
alight  on  the  lower  petal  (labellum),  which  suddenly  curves  down- 
ward, taking  the  bee  far  below  the  stigmatic  surface.  As  the  bee 
enters  the  flower  it  brushes  against  the  pollen  mass  and  removes 
some  of  it,  but  as  it  was  immediately  lowered  it  could  not  rub 
this  pollen  onto  the  stigma  while  it  was  taking  the  nectar.  But 
as  it  visits  the  next  flower,  when  it  first  enters  some  of  the  pollen 
from  the  previous  flowrer  is  brushed  off  on  the  stigma.  Interesting 
experiments  can  be  made  on  some  of  the  orchids  growrn  in  green- 
houses with  a  lead  pencil  or  other  slender-pointed  instrument  to 
imitate  the  movement  of  the  proboscis  of  an  insect.  Some  of  the 
native  orchids  can  be  used  to  demonstrate  the  methods  of  cross- 
pollination. 

296.   Flowers  constructed  to  lead  the  insect  in  at  one 
point  and  out  at  another. — Some  of  our  native  species  illustrate 

*  Darwin's  work  "On  the  Fertilization  of  Orchids  by  Insects"  should  be 
consulted.     Full  descriptions  and  illustrations  are  given. 


METHODS  OF  POLLINATION 


179 


Fig.  138. 
Cypripedium. 


this.  One  species  of  the  lady-slipper  (Cypripedium)  is  shown 
in  fig.  138.  The  insect  enters  about  the  middle  of  the  boat-shaped 
labellum.  In  going  out  it  passes 
up  and  out  at  the  end  near  the 
flower  stalk.  In  doing  this  it 
passes  the  stigma  first  and  the  an- 

ther last,  rub- 

bing    against 

both.     The 

pollen  caught 

on  the  head  of 

the  insect  will 

not  touch  the  .  ^ 

bection  of  flower  of  Cypnpedium.     st, 
nf    the    stigma;  a,  at  the  left  stamen.     The  insect 
c    enterg  the  labellum   at  the  center)  passes 

flower     under  and   against   the   stigma,   and   out 

lower,  thrc?ugh  the*opening  b   *her'e  it  rubs 

but  \vill   be   in    against  the   pollen.     In   passing   through 
l    another  flower  this  pollen  is  rubbed  off  on 
position  to    the  stigma- 

come  in  contact  with  the  stigma  of  the  next  flower  visited. 

297.  Pollination  of  the  Smyrna  fig.  —  Figs  have  been  culti- 
vated in  parts  of  the  United  States  for  many  years,  in  the  Gulf 
and  Atlantic  States  and  in  California.  But  the  variety  which 
has  been  in  successful  cultivation  during  most  of  this  period  is 
inferior  to  the  imported  figs.  Consequently  they  could  not  come 
into  successful  competition  with  the  superior  imported  variety,  the 
Smyrna  or  Turkey  figs.  Nevertheless  they  have  been  grown  in 
considerable  numbers  for  home  use  by  the  cultivators.*  Because 
of  the  inferior  quality  of  the  figs  in  cultivation  here,  a  number  of 
attempts  have  been  made  during  the  last  forty  years  to  introduce 
the  Smyrna  fig  into  cultivation  in  California.  Trees  were  suc- 
cessfully grown,  but  they  failed  to  mature  fruit,  the  young  figs 
falling  early  from  the  trees. 

*  This  variety  of  the  fig  belongs  to  the  same  species  as  the  Smyrna  fig 
(Ficus  carica),  but  the  flowers  are  modified  and  sterile  (often  called  popu- 
larly "mule"  flowers),  and  the  fruit  has  taken  on  the  habit  of  forming  with- 
out fertilization.  This  variety  is  also  grown  to  some  extent  in  Southern 
Europe. 


i8o 


GROWTH   AND    WORK   OF  PLANTS 


The  cause  of  this  lay  in  the  fact  that  the  Smyrna  fig  produces 
only  pistillate  flowers.  To  set  fruit  they  must  be  pollinated  from 
a  pollen-producing  variety.  In  the  Mediterranean  region  where 
Smyrna  figs  are  grown,  the  pollen  for  this  purpose  comes  from  a 
wild  fig  called  the  caprifig,  which  is  the  staminate  form  of  this 
species  and  of  course  bears  the  pollen.  From  very  ancient  times 
it  has  been  the  custom  in  Oriental  regions  to  gather  branches  of 


Fig.  140. 

The  fig.    A,  branch  bearing  a  fig;  B,  section  of  fig  showing  flowers  within; 
C,  staminate  flower;  £>,  pistillate  flower. — After  Wossidlo. 

the  caprifig  and  hang  them  in  the  trees  of  the  edible  fig  during  the 
season  when  the  latter  is  in  flower.  From  these  caprifigs  a  small 
insect  issues,  called  the  fig-fertilizing  insect  (Blastophaga).  In 
coming  out  of  the  caprifig  it  drags  out  with  it  quantities  of  pollen. 
It  then  visits  the  pistillate  flowers  of  the  Smyrna  fig,  in  which  the 
branches  are  hung,  and  those  near  by,  for  the  purpose  of  deposit- 
ing its  eggs.  In  doing  this  it  crawls  over  the  pistillate  flowers 
and  brushes  off  pollen  of  the  caprifig  in  them. 

In  the  home  of  the  Smyrna  fig  there  are  said  to  be  three  genera- 
tions of  fruit  on  the  caprifig,  the  spring  and  early  summer  crop, 
known  as  the  profichi,  the  midsummer  crop,  the  mammoni,  and 
the  autumn  crop,  mamme,  the  latter  remaining  on  the  trees  all 
winter.  The  insect  hibernates  in  the  mamme.  In  the  spring  it 


METHODS  OF  POLLINATION  l8l 

comes  out  and  deposits  its  eggs  in  the  profichi.  By  the  time  this 
generation  is  ready  to  come  out  the  flowers  of  the  Smyrna  fig  are 
ready  for  pollination.  Many  of  the  insects  of  the  profichi  genera- 
tion, which  are  in  the  fruits  left  on  the  caprifigs,  lay  their  eggs 
in  the  second  crop,  the  mammoni,  and  those  issuing  from  these 
deposit  their  eggs  in  the  mamme.  In  this  way  the  insects  con- 
tinue their  existence  from  year  to  year  in  great  numbers  in  the 
caprifig.  About  1882  a  large  number  of  Smyrna  fig  trees  were 
started  in  California.  But  they  bore  no  fruit.  A  few  years  later 
another  attempt  was  made  and  the  caprifig  as  well  as  the  Smyrna 
fig  was  introduced  by  cuttings.  But  as  the  insect  was  not  present, 
failure  again  resulted.  For  a  few  years  some  Smyrna  figs  were 
produced  by  artificial  pollination  with  pollen  from  the  caprifig. 
Attempts  were  then  made  to  introduce  the  fig-fertilizing  insect. 
In  1898  to  1900  this  was  successful  and  Smyrna  figs  were  produced 
through  the  agency  of  this  insect  which  were  equal  in  quality  to 
the  imported  figs.*  Their  culture,  therefore,  promises  to  become 
a  valuable  industry  in  California  and  some  of  the  Southwestern 
States  if  proper  attention  is  given  to  it.  The  process  of  hanging 
the  branches  of  fruit  of  the  caprifig  in  the  Smyrna  fig  trees  is  called 
caprification. 

298.  The  fruit  of  the  fig  is  peculiar.  It  is  the  enlarged 
fleshy,  somewhat  pear-shaped  receptacle,  the  end  of  a  shoot,  which 
is  hollow,  and  the  numerous  flowers  are  borne  over  the  surface  of 
this  hollow.  The  "  seeds  "  are  small,  hard  nutlets,  and  each  one 
is  in  reality  a  small  fruit,  the  seed  being  united  with  the  wall  of 
the  ovary.  It  is  said  that  the  "  seed  "  gives  the  flavor  to  the 
Smyrna  fig. 

*  L.  O.  Howard,  Smyrna  Fig  Culture  in  the  United  States,  Year  Book  of 
the  United  States  Department  of  Agriculture,  79-106,  pis.  1-8,  and  text 
figs.  1900. 


CHAPTER  XIX. 
FERTILIZATION  AND   DEVELOPMENT   OF    THE  SEED.* 

299.   Fertilization  consists  in  the  union  of  two  cells,  or  of  the 
nuclei  of  two  cells  of  a  different  nature,  a  sperm  or  male  nucleus 
with  an  egg  or  female  nucleus.     The  result  is  a  stimulus  or  impulse 
given  to  the  fertilized  egg  to  develop  and  form  an 
embryo  plant  which  later  can  develop  into  a  plant 
like    the  parent.     The    male,    nucleus,    or   sperm 
nucleus,  is  derived   from  the   pollen  grain"  which 
is  formed  in  the  anther  of  the  stamen.     The  egg 
Fig.  141.         is  developed  in  the  embryo  sac  within  the  ovule, 
poi£iagrain™ftriie  which  is  in  turn  formed  in  the  ovary,  a  part  of 

Hum.    The  smaller     ,  i  •   ,-\ 

cell  is  the  genera-    the  pistil. 

300.  The  formation  of  the  pollen,  the  sperm 
cells,  and  pollen  tube. — The  pollen  is  formed,  as  we  have  seen,  in 
the  anther.  When  the  pollen  grain  is  very  young  it  consists  of  a 
free  cell  in  the  pollen  sac.  The  cell  wall  encloses  the  protoplasm, 
the  living  substance,  and  within  this  is  a  very  important  organ  of  the 
cell,  the  nucleus,  wrhich  is  a  more  or  less  rounded  body,  finely  granu- 
lar and  usually  appearing  denser  than  the  protoplasm.  As  the  pol- 
len grain  ripens  a  change  takes  place  in  its  contents  as  follows.  The 
nucleus  divides  into  two  nuclei,  and  very  often  a,  curved  thin  cell 
wall  is  formed  separating  a  small  mass  of  the  protoplasm  with  one 
nucleus  from  the  larger  mass  containing  the  other  nucleus,  as  shown 

*  The  study  of  the  processes  of  fertilization  and  the  development  of  the  seed 
requires  special  preparation  of  material  and  the  use  of  technical  methods 
which  could  not  be  employed  by  students  in  the  first-year  course.  It  is 
desirable,  however,  that  students  should  have  a  general  knowledge  of  these 
processes.  This  chapter  is  presented  for  this  purpose.  It  can  be  supple- 
mented, if  desirable,  by  demonstrations  of  microscopic  material  prepared 
by  the  teacher  or  purchased  for  the  purpose. 

182 


FERTILIZATION  AND  DEVELOPMENT  OF  SEED       183 


in  fig.  141.  Very  soon  this  smaller  cell  becomes  free  and  its  pro- 
toplasm floats  in  the  protoplasm  of  the  larger  cell.  This  is  the 
condition  in  which  most  ripe  pollen  grains  are;  there  are  two  cells, 
one  floating  within  the  protoplasm  of 
the  larger  one.  The  larger  cell  is 
sometimes  called  the  tube  cell  because 
later  it  grows  out  into  the  pollen  tube. 
The  smaller  one  floating  within  the 
larger  one  is  called  the  generative  or 
body  cell*  After  a  pollen  grain  falls  on 
the  stigma  it  germinates  and  forms  a 
long  tube  which  grows  down  through 
the  style  into  the  ovary,  where  it  enters 
the  ovule.  The  two  nuclei  move  into 
the  pollen  tube.  The  nucleus  of  the  grain- 
body  cells  divide  into  two  nuclei  either  in  the  tube  or  before  enter- 
ing it.  These  two  nuclei  are  the  sperm  nuclei,  or  male  nuclei,  and 
they  are  brought  into  the  ovule  by  the  pollen  tube. 

301.  Structure  of  the  ovule. — The  ovule  is  nearly  oval  in 
form.  There  are  usually  two  coats  on  the  ovule,  but  sometimes 
only  one.  Except  at  the  stalk  end  where  the  tissues  are  more  rr 


Fig.  143. 

A  represents  a  straight  (orthotropus)  ovule  of  Polygonum;  B,  the  inverted  (anatropus)  ovule 
of  the  lily;  and  C,  the  right-angled  (campylptropus)  ovule  of  the  bean;  /,  funicle;  c,  chalaza; 
k,  nucellus;  ai,  outer  integument;  ii,  inner  integument;  m,  micropyle;  em,  embryo  sac. 

less  blended,  the  coats  of  the  ovule  can  be  seen  in  a  lengthwise 
section  as  two  distinct  layers  of  tissue,  but  there  is  •  a  circular 

*  Or  central  cell  of  the  antheridium.     See  Chapter  XXXV. 


1 84 


GROWTH  AND    WORK   OF   PLANTS 


In 


opening  at  the  apex  of  the  ovule,  so  that  there  is  a  communication 

from  the  outside.     This  opening  is  the  micropyle.     The  stalk  of 

the  ovule  attaches  it  to 
the  wall  of  the  ovary. 
a  straight  ovule  the 
stands  out  straight  in  line 
with  its  stalk.  In  a  right- 
angled  ovule  the  stalk 
is  bent  over  at  the  upper 
end,  so  that  the  ovule 
stands  about  at  right 
angles.  In  the  inverted 
ovule  the  upper  end  of 
the  stalk  is  bent  so  strongly 
that  the  ovule  is  inverted 
and  the  stalk  is  then  fused 
with  the  side  of  the  ovule. 
This  part  of  the  stalk  is 
called  the  raphe  (see  fig. 
143  for  details). 

302.  The  embryo  sac 
and  egg.  —  At  the  close 
of  the  development  of 
the  ovule  a  sac  is  formed 
within  it,  known  as  the 
embryo  sac.  This  em- 
bryo sac  contains  sev- 
eral nuclei,  usually  eight, 
lying  in  the  protoplasm. 
One  of  these  eight  nu- 

clei in  the  embryo  sac,  with  the  protoplasm  around  it,  is  the 

egg  cell. 

303.   Fertilization.  —  When  the  pollen  tube  grows  into   the 

ovule  at  the  micropyle  it  enters  the  embryo  sac,  into  which  it 

empties  the  two  sperm  nuclei.     One  of  these  s.perm  nuclei  fuses 

with  the  egg  nucleus.     This  is  fertilization. 


Fig.  144. 

iry  and 

of  fertilization  in  angiosperm.  /,  funicle  of  ovule;  n, 
nucellus;  m,  micropyle;  b,  antipodal  cells  of  embryo 
sac;  e,  endosperm  nucleus;  k,  egg  cell  and  synergids; 
ai,  outer  integument  of  ovule;  «,  inner  integument. 
The  track  of  the  pollen  tube  is  shown  down  through 
the  style,  walls  of  the  ovary  to  the  micropylar  end  of 
the  embryo  sac. 


FERTILIZATION  AND  DEVELOPMENT  OF  SEED       1 8$ 


304.  Development  of  the  embryo. — The  fertilized  egg  now 
grows  and  divides  into  two  cells,  and  these  into  more  cells,  forming 
the  young  embryo  which  lies  in  the  sac  within  the  ovule.     This 
is  why  the  term  embryo  sac  is  employed  for  this  structure.     At  the 
time  of  fertilization  the  endosperm  begins  to  form,  and  develops 
the  tissue,  some  of  which  is  used  in  the  growth  of  the  embryo,  and 
the  rest  is  stored  as  food,  either  by  the  side  of  or  around  the  embryo, 
or  in  the  cotyledons,  according  to  the  kind  of  seed,  for  use  by  the 
young  seedling. 

305.  Formation  of  the  seed. — We  are  now  ready  to  learn 
how  the  seed  is  formed.     In  the  bean,  pea,  squash,  and  many 
other  seeds,  the  embryo  uses  up  all  of  the  endosperm  which  is 
formed,  storing  up  in  the  cotyledons  what  is  not  used  in  making 
the  tissues  of  the  different  parts  of  the  embryo.     During  this 
process  nearly  or  quite  all  of  the  inside  portion  of  the  ovule  has 
been  used  as  food  for  the  developing  endosperm.     There  remain 


Fig.  145- 

Seed'  of  violet,  external  view,  and 
section.  The  section  shows  the  embryo 
lying  in  the  endosperm. 


Fig.  146. 

Section  of  fruit  of  pepper  (Piper 
nigrum),  showing  small  embryo  lying 
in  a  small  quantity  of  whitish  endo- 
sperm at  one  end,  the  perisperm 
occupying  the  larger  part  of  the  in- 
terior, surrounded  by  pericarp. 


then  the  walls  of  the  ovule  (the  integuments),  which  make  the 
walls  of  the  seed.  Inside  lies  the  embryo,  with  sometimes  a  papery 
remnant  of  the  interior  of  the  ovule,  as  in  the  squash,  pumpkin, 
etc.  In  the  forming  grain  of  corn,  wheat,  castor  bean,  etc.,  the 
embryo  uses  up  only  a  portion  of  the  endosperm,  so  that  in  the 
seed  there  are  embryo  and  endosperm,  surrounded  by  the  walls  of 
the  ovule;  the  embryo  and  endosperm  with  the  enveloping  ovule 


1 86  GROWTH  AND    WORK   OF  PLANTS 

walls  make  the  seed;  but  in  the  grain  of  wheat,  corn,  etc.,  the  wall 
of  the  ovary  is  fused  with  the  walls  of  the  ovule,  making  the  ripe 
grain.  In  the  water  lily,  the  pepper,  and  some  other  plants,  a  part 
of  the  interior  of  the  ovule  is  left  in  the  seed.  This  is  called  peri- 
sperm  when  it  is  present  in  the  seed,  so  that  in  such  a  seed  there 
are  embryo,  endosperm,  and  perisperm  surrounded  by  the  integu- 
ments or  ovule  walls. 

306.  Albuminous  and  exalbuminous  seeds. — In  the  study 
of  the  substances  stored  in  the  grain  of  corn  and  wheat  it  was 
found  that  there  is  a  large  quantity  of  starch  in  the  endosperm. 
This  is  an  albuminous  substance.  Seeds  containing  endosperm 
at  ripeness  are  called  albuminous  seeds,  while  those  like  the  bean, 
pea,  etc.,  with  no  endosperm  are  called  exalbuminous. 


CHAPTER  XX. 

THE  FRUIT. 
I.  PARTS  OF  THE  FRUIT. 

307.  The  fruit  of  the  plant  is  the  final  result  of  the  work  of 
the  flower.     The  seed  is  formed  in  connection  with  the  fruit, 
usually  within  the  fruit.     It  is  the  end  or  aim  for  which  the  plant 
throughout  its  life  has  been  working,  in  order  that  through  the 
seed  the  plant  may  be  multiplied,  distributed,*  and  invigorated. 
The  word  seed  is  often  used  to  denote   any  reproductive   body 
which  may  be  planted  or  "  sown  "  to  reproduce  that  plant  again. 
In  a  strict  sense,  however,  seeds  are  only  formed  by  the  true  seed 
plants,  f    The  seed  in  this  sense  consists  of  the  ripened  ovule 
containing  the  embryo  plant.     The  ovule  has  one  or  two  coats 
(integuments )      ( fi  g . 

143)  which  become 
in  the  ripe  seed  the 
seed  coats.  The 
ovule  is  formed  with- 
in the  ovary.  In 
many  plants  the  walls 
of  the  ovule  are  free 
from  the  wall  of  the  Fig.  147. 

OVary,  as  in  the    pea,    at  rfghtf^ne^in  °section r shewing aSe  'seed  Se^thl  3d 

bean,  etc,  so  that  the  ovarywalh 

seed  when  ripe   becomes  free  from  the  wall  of  the  ovary  and 

separates  by  the  splitting  of  the  fruit. 

308.  The  fruit  consists  of  the  ripened  ovary  including  the 
seed,  and  in  many  cases  other  accessory  parts  of  the  flower  as 

*  It  must  be  remembered  that  many  plants  multiply  and  become  dis- 
tributed in  other  ways  also. 

t  The  Spermatophyta,  including  the  gymnosperms  and  angiosperms. 

187 


188 


GROWTH   AND   WORK   OF  PLANTS 


calyx,  receptacle,  etc.,  combined  with  it.  The  fruit  may  be 
formed  of  a  single  simple  pistil  or  it  may  be  formed  of  several 
simple  pistils  crowded  together  (aggregate,  or  collective  fruits),  or 
there  may  be  accessory  parts  of  the  flower  which  reinforce  the 
fruit  (accessory  or  reinforced  fruits). 

309.  The  pericarp. — The  wall  of  the  ripened  ovary  is  called 
the  pericarp.     It  is  the  part  of  the  fruit  which  envelops  the  seed, 

and  may  consist  of  the  car- 
pels alone,  or  of  the  carpels 
and  the  adherent  part  of 
the  receptacle,  or  calyx.  In 
many  fruits  the  pericarp 
shows  a  differentiation  into 
layers,  or  zones  of  tissue, 
as  in  the  cherry,  peach,  plum, 
etc.  The  outer,  which  is  here 
soft  and  fleshy,  is  exocarp, 
while  the  inner,  which  is 
hard,  is  the  endocarp.  An 
intermediate  layer  is  some- 
times recognized  and  is 
called  mesocarp.  In  such 
cases  the  skin  of  the  fruit 
is  recognized  as  the  epicarp. 

Epicarp    and    mesocarp    are    more    often    taken    together    as 

exocarp. 

310.  In  general,  fruits  are  dry  or  fleshy.     Dry  fruits  may 
be  grouped  under  two  heads.     Those  which  open  at  maturity 
and  scatter  the  seed  are   dehiscent.     Those  which  do  not  open 
are  indehiscent. 

II.    INDEHISCENT  FRUITS. 

311.  The  akene.— The  thin,  dry  wall  of  the  ovary  encloses  the 
single  seed.     It  usually  does  not  open  and  free  the  seed  within. 
Such  a  fruit  is  an  akene.     An  akene  is  a  small,  dry,  one-seeded, 
indehiscent  fruit.     All  of  the  crowded  but  separate  pistils  in. the 


Fig.  148. 

Section  of  drupe,  or  stone  fruit  of  peach, 
showing  the  fleshy  exocarp,  stony  endocarp,  and 
the  "meat"  or  embryo  within. 


THE   FRUIT:   INDEHISCENT   FRUITS 


189 


buttercup  flower  when  ripe  make  a  head  of  akenes,  which  form 
the  fruit  of  the  buttercup  (fig.  147).  Other  examples  of  akenes 
are  found  in  other  members  of  the  buttercup  family,  also  in  the 
composites,  etc.  The  sunflower  seed  is  a  good  example  of  an 
akene.  It  should  be  borne  in  mind  that  the  sunflower  "  seed  " 
(and  "  seed  "  of  other  composite  flowers)  is  a  fruit  containing  the 
seed. 

312.  The  samara. — The  samara  is  a  dry  fruit,  with  a  thin 
membranous  expansion  extending  more  or  less  around  the  edge, 
somewhat    resembling    wings,    which 

serve  to  float  the  seed  and  aid  in  dis- 
tribution by  the  wind.  The  "winged" 
fruits  of  the  maple,  box  elder  (fig.  149), 
elm,  etc.,  are  examples.  They  are 
sometimes  called  "  key^"  fruits. 

313.  The  caryopsis  is  a  dry  fruit 
in  which  the  seed  is  united  with  the 
pericarp  (wall  of  the  ovary),  as  in  the 
wheat,  corn,  and  other  grasses.     It  is 
perfectly  proper  to  say  "  seed  wheat," 
"  seed  corn,"  "  grass  seed,"  etc.,  if  it 
is   understood   that   these   grains   are 
fruits  including  the  seed.     It  would  be 
absurd  to  insist  that  in  all  such  cases 
one  must  avoid  the  use  of  the  term  seed 
when  speaking  of  the   grains  and  of 

akenes,  and  use  instead  sunflower  fruit,  wheat  fruit,  corn  fruit, 
grass  fruit,  etc.,  or  oat  fruit  and  barley  fruit.  In  the  latter 
"  seeds  "  not  only  are  the  seed  coats  united  with  the  pericarp, 
but  this  is  firmly  enclosed  within  the  palae  of  the  flower. 

314.  The  schizocarp  is  a  dry  fruit  consisting  of  several  united 
carpels  (compound  pistil)  which  splits  at  maturity  in  such  a  way  that  the 
carpels  separate  from  each  other  but  do  not  themselves  dehisce  and  free  the 
seed,  as  in  the  carrot  family,  mallow  family. 

315.   The  acorn. — The  acorn  fruit  consists  of  the  acorn  and 
the  "  cup  "  at  the  base  in  which  the  acorn  sits.     The  cup  is  a 


Fig.  149. 

A    winged    fruit,   a   samara, 
fruit  of  the  box  elder. 


190 


GROWTH   AND    WORK   OF   PLANTS 


I 


curious  structure,  and  is  supposed  to  be  composed  of  a  crown  of 
numerous  small  leaves  (involucre)  at  the  base  of  the  pistillate 

flower,  which  become  united 
into  a  hard  cup-shaped  body. 
When  the  acorn  is  ripe  it 
easily  separates  from  the  cup, 
but  the  hard  pericarp  forming 
the  "shell"  of  the  acorn 
remains  closed.  Frost  may 
cause  it  to  crack,  but  very 
often  the  pericarp  is  split  open 
at  the  smaller  end  by  the 
wedge-like  pressure  exerted 
by  the  emerging  root  during 
germination. 

316.  The hazelnut,  chest- 
nut, and  beechnut. — In  these 
fruits  a  crown  of  leaves  (invo- 
lucre) at  the  base  of  the  flower 

grows  around  the  nut  and  completely  envelops  it,  forming  the  husk 
or  burr.  When  the  fruit  is  ripe  the  nut  is  easily  shelled  out 
from  the  husk.  In  the  beechnut  and  chestnut  the  burr  dehisces 
as  it  dries  and  allows  the  nut  to  drop  out.  But  the  fruit  is  not 
dehiscent,  since  the  pericarp  is  still  intact  and  encloses  the 
seed. 

317.  The  hickory  nut,  walnut,  and  butternut. — In  these 
fruits  the  "  shuck  "  of  the  hickory  nut  and  the  "  hull  "  of  the 
walnut  and  butternut  are  different  from  the  involucre  of  the  acorn 
or  hazelnut,  etc.  In  the  hickory  nut  the  "  shuck  "  probably 
consists  partly  of  calyx  and  partly  of  involucral  bracts  consoli- 
dated, probably  the  calyx  part  predominating.  This  part  of  the 
fruit  splits  open  as  it  dries  and  frees  the  "  nut,"  the  pericarp  being 
very  hard  and  indehiscent.  In  the  walnut  and  butternut  the 
"  hull  "  is  probably  of  like  origin  as  the  "  shuck  "  of  the  hickory 
nut,  but  it  does  not  split  open  as  it  ripens.  It  remains  fleshy. 
The  walnut  and  butternut  are  often  called  drupes  or  stone- 


Fig.  150. 

Fruit  of  corn,  husks  spread  to  show  ear. 


THE   FRUIT:   DEHISCENT   FRUITS 


Loo 

Fig.  151. 

Diagrams  illustrating  three  types  (in  cross 
section)  of  the  dehiscence  of  dry  fruits.  Loc,  loculi- 
cidal;  Sep,  Septicidal,  Septifragal. 


fruits,  but  the  fleshy  part  of  the  fruit  is  not  of  the  same  origin 
as  the  fleshy  part  of  the  true  drupes,  like  the  cherry,  peach, 
plum,  etc. 

III.    DEHISCENT  FRUITS. 
Of  the  dehiscent  fruits  several  prominent  types  are  recognized. 

318.   The  capsule.    When  - 

the  capsule  is  syncarpous  (com-         /\    ^\ 

pound  pistil)  it  may  dehisce  in  j        ' 

three  different  ways:    ist.  The          \-i^/ 

carpels  split  along  the  line  of 

their    union    with    each   other 

longitudinally,  as  in  the  azalea 

or  rhododendron.  2d.  The  car- 
pels split  down  the  middle  line,  as  in  the  fruit  of  the  iris,  lily,  etc.  3d.  The 

carpels  open  by  pores,  as  in  the 
poppy.  Some  syncarpous  capsules 
have  but  one  locule,  the  partitions 
between  the  different  locules  when 
young  having  disappeared.  The 
"bouncing-bet"  is  an  example, 
and  the  seeds  are  attached  to  a 
central  column  in  four  rows  corre- 
sponding to  the  four  locules  present 
in  the  young  stage. 

319.  A     follicle    is    a    cap- 
sule with  a   single    carpel   which 
splits  open  along   the  ventral  or 
upper  suture,   as  in  the  larkspur, 
peony. 

320.  The  legume,  or  true 
pod,js  a  capsule  with  a  single 
carpel  which  splits  along  both 
sutures,    as    the    pea,    bean, 
vetch,  etc.     As  the  pod  ripens 
and  dries,   a  strong    twisting 


Fig.  152. 
Pods  of  Sweet  Pea. 


tension    is    often    produced, 
which  splits  the  pod  suddenly,  scattering  the  seeds. 

321.   The  silique.       In  the  toothwort,  shepherd's-purse,    and    nearly 
all  of  the  plants  in  the  mustard  family,  the  fruit  consists  of  two  united  car- 


1 92  GROWTH   AND    WORK   OF   PLANTS 

pels,  which  separate  at  maturity,  leaving  the  partition  wall  persistent.     Such 
a  fruit  is  a  silique;  when  short  it  is  a  silicle,  or  pouch. 

322.  A  pyxidium,  or  pyxis,  is  a  capsule  which  opens  with  a  lid,  as  in  the 
plantain. 

IV.    FLESHY  AND   JUICY   FRUITS. 

323.  The  drupe,  or  stone-fruit. — In  the  plum,  cherry,  peach, 
apricot,  etc.,  the  outer  portion  (exocarp)  of  the  pericarp  (ovary) 
becomes  fleshy,  while  the  inner  portion  (endocarp)  becomes  hard 
and  stony  and  encloses  the  seed,  or  "  pit "  (figs.  148,  153).     Such 
a  fruit  is  known  as  a  drupe,  or  as  a  stone-fruit.     In  the  almond 
the  fleshy  part  of  the  fruit  is  removed. 


Fig.  153- 
Peach  pit,  the  hard  endocarp  split  open,  showing  the  embryo  within. 

m 

324:.  The  raspberry  and  blackberry. — While  these  fruits  are 
known  popularly  as  "  berries,"  they  are  not  berries  in  the  technical 
sense.  Each  ovary,  or  pericarp,  in  the  flower  forms  a  single  small 
fruit,  the  outer  portion  being  fleshy  and  the  inner  stony,  just  as  in 
the  cherry  or  plum.  It  is  a  drupelet  (little  drupe).  All  of  the 
drupelets  together  make  the  "  berry,"  and  as  they  ripen  the  sepa- 
rate drupelets  cohere  more  or  less.  It  is  a  collection,  or  aggrega- 
tion, of  fruits,  and  consequently  they  are  sometimes  called  collective 
fruits,  multiple  or  aggregate  fruits.  In  the  raspberry  the  fruit 
separates  from  the  receptacle,  leaving  the  latter  on  the  stem,  while 


THE  FRUIT:  FLESHY  AND   JUICY  FRUITS         193 


Cluster  of  blackberry  fruits,  aggregate  fruits. 


Fig.  155. 


Blackberry  fruit,  aggregate  fruit;  at  left,  the  fleshy  part  of  receptacle  bearing  the  drupelets 
is  removed,  showing  the  dead  and  withered,  persistent  stamens;  at  the  center,  the  fruit  is  cut 


to  show  the  fleshy  receptacle. 


194 


GROWTH   AND    WORK   OF   PLANTS 


the  drupelets  of  the  blackberry  and  dewberry  adhere  to  the  recep- 
tacle and  the  latter  separates  from  the  stem. 


Fig.  156. 
Aggregate  fruit  of  raspberry;  at  left,  the  drupelets  removed,  showing  the  persistent  receptacle. 


325.  The  berry. — In  the  true  berry  both  exocarp  (including 
mesocarp)  and  endocarp  are  fleshy  or  juicy.  Good  examples  are 
found  in  cranberries,  huckle- 
berries, currants,  snowberries, 
tomatoes,  etc.  The  calyx  and 
wall  of  the  pistil  are  adnate, 
and  in  fruit  become  fleshy  so 
that  the  seeds  are  imbedded  in 
the  pulpy  juice.  The  seeds 
themselves  are  more  or  less 
stony.  In  the  case  of  berries, 
as  well  as  in  strawberries,  rasp- 


berry. 

berries,   and   blackberries,   the 

fruits  are  eagerly  sought  by  birds  and  other  animals  for  food. 
The  seeds  being  hard  are  not  digested,  but  are  passed  with  the 
other  animal  excrement  and  thus  gain  dispersal. 


THE   FRUIT:    REINFORCED    FRUITS 


195 


V.    REINFORCED,   OR  ACCESSORY,   FRUITS. 

326.  When  the  receptacle  is  grown  to  the  pericarp  in  fruit, 
the  fruit  is  said  to  be  reinforced.     The  receptacle  may  enclose  the 
pericarp,  or  the  latter  may  be 

seated  upon  the  receptacle. 

327.  In  the  strawberry  the 
receptacle  of  the  flower  becomes 
large    and    fleshy,    while    the 
"  seeds,"  which  are  akenes,  are 
sunk    in  the   surface    and  are 
hard  and  dry.     The  strawberry 
thus  differs  from  the  raspberry 
and  blackberry,  but  like  them 
it  is  not  a  true  berry. 

328.  The     apple,     pear, 
quince,    etc. — In   the    flower 
the  calyx,  corolla,  and  stamens 
are    perigynous,   i.e.,   they  are 

seated  on  the  margin  of  the  receptacle,  which  is  elevated  around 

the  pistils.  In  fruit  the 
receptacle  becomes  con- 
solidated with  the  wall 
of  the  ovary  (with  the 
pericarp).  The  recepta- 
cle thus  reinforces  the 
pericarp.,  The  recepta- 
cle and  outer  portion 
of  the  pericarp  become 
fleshy,  while  the  inner 
portion  of  the  pericarp 
becomes  papery  and 
f orms  the  "  core."  The 
calyx  persists  on  the  free  end  of  the  fruit.  Such  a  fruit  is  called  a 
pome.  The  receptacle  of  the  rose-flower,  closely  related  to  the 


Fig.  158. 
Section  of  tomato  fruit. 


Fig.  159- 
Fruit  of  squash,  a  pepo. 


196 


GROWTH   AND    WORK   OF   PLANTS 


Fig.  1 60. 
Section  of  squash  fruit. 


apple,  is  instructive  when  used  in 
comparison.  The  rose-fruit  is 
called  a  "  hip." 

329.  Thepepo. — The  fruit  cf 
the  squash,  pumpkin,  cucumber, 
etc.,  is  called  a  pepo.  The  outer 
part  of  the  fruit  is  the  receptacle, 
which  is  consolidated  with  the 
outer  part  of  the  three-loculed 
ovary.  The  calyx,  which,  with  the 
corolla  and  stamens,  is  attached 
to  the  upper  part  cf  the  ovary, 
falls  off  from  the  young  fruit. 


VI.    FRUITS   OF   GYMNOSPERMS. 

330.  The  fruits  of  the  gymnosperms  differ  from  nearly  all  cf 
the  angiosperms  in  that  the  seed  formed  from  the  ripened  ovule 
is  naked  from  the  first,  i.e.,  the  ovary,  or  carpel,  does  not  enclose 
the  seed. 

331.  The  cone-fruit  is  the  most  prominent  fruit  of  the  gymno- 
sperms, as  can  be  seen  in  the  cones  of  various  species  of  pine, 
spruce,  balsam,  etc. 

332.  Fleshy    fruits    of    the    gymnosperms. — Seme  cf   the 
fleshy  fruits  resemble  the  stone-fruits  and  berries  of  the  angio- 
sperms.    The  cedar  "  berries,"  for  exampl^^'e  fleshy  and  contain 
several  seeds.     But  the  fleshy  part  of  the  fruit  is  formed,  not 
from  pericarp,  since  there  is  no  pericarp,  but  from  the  outer  por- 
tion of  the  ovule,  while  the  inner  portion  of  the  ovule  forms  the 
hard  stone  surrounding  the  endosperm  and  embryo.     An  exami- 
nation of  the  pistillate  flower  of  the  cedar  (juniper)  shows  usually 
three  flask-shaped  ovules  on  the  end  of  a  fertile  shoot  subtended 
by  as  many  bracts.     The  young  ovules  are  free,  but  as  they  grow 
they   coalesce,   and  the    outer   walls   become    fleshy,   forming   a 
berry-like  fruit  with  a  three-rayed  crevice  at  the  apex  marking 
the  number  of  ovules.     The  red  fleshy  fruit  of  the  yew  (Taxus) 


THE  FRUIT:   "FRUIT"  OF  FERNS,  MOSSES,  ETC. 

resembles  a  drupe  which  is  open  at  the  apex.  The  stony  seed  is 
formed  from  the  single  ovule  on  the  fertile  shoot,  while  the  red  cup- 
shaped  fleshy  part  is  formed  from  the  outer  integument  of  the 
ovule.  The  so-called  "  aril  "  of  the  young  ovule  is  a  rudimentary 
outer  integument. 

333.  The  fruit  of  the  maidenhair  tree  (Ginkgo)  is  about  the 
size  of  a  plum  and  resembles  very  closely  a  stone-fruit.     But  it  is 
merely  a  ripened  ovule,  the  outer  layer  becoming  fleshy  while  the 
inner  layer  becomes  stony  and  forms  the  pit  which  encloses  the 
embryo  and  endosperm.     The  so-called   "  aril,"  or  "  collar,"  at 
the  base  of  the  fruit  is  the  rudimentary  carpel,  which  sometimes  is 
more  or  less  completely  expanded  into  a  true  leaf.     The  fruit  of 
Cycas  is  similar  to  that  of  Ginkgo,  but  there  is  no  collar  at  the  base. 
In  Zamia  the  fruit  is  more  like  a  cone,  the  seeds  being  formed, 
however,  on  the  under  sides  of  the  scales. 

VII.    THE   "FRUIT"   OF   FERNS,  MOSSES,  ETC. 

334.  The  term  "  fruit  "  is  often  applied  in  a  general  or  popular 
sense  to  the  groups  of  spore-producing  bodies  of  ferns  (fruit-dots, 
or  sori),  to  the  spore  capsules  of  mosses  and  liverworts,  and  also  to 
the  fruit-bodies,  or  spore-bearing  parts,  of  the  fungi  and  algae. 


CHAPTER   XXI. 
SEED   DISPERSAL. 

335.  Necessity  for  distribution  of  seed. — While  the  forma- 
tion of  seed  is  the  end  towards  which  the  energy  of  the  plant  is 
directed,  this  energy  would  be  almost  wholly  misspent  were  there 
no  means  for  the  distribution  of  the  seed  over  the  surface  of  the 
earth.     Were  there  no  means  for  the  natural  distribution  of  seed, 
the  seed  would  fall  to  the  ground  from  the  plant  where  it  was  pro- 
duced.    Extension  of  the  plant  over  new  territory  would  only 
progress  so  far  as  the  branches  reached.     This  would  be  tedious 
and  very  slow  and  would  not  enable  the  plant  to  multiply  itself 
rapidly  enough  to  maintain  its  hold.     The  present  wide  distri- 
bution and  great  variety  of  plant  life  on  the  globe  would  have  been 
impossible. 

336.  To  succeed  in  filling  their  place  in  nature  plants  must 
be  in  a  position  to  throw  vast  quantities  of  seed  into  any  territory 
which   becomes  unoccupied,   or  into   new   territory  each   year. 
Since  they  do  not  possess  the  intelligence  of  man  whereby  they 
might  discover  unoccupied  territory  and  bend  their  energies  to 
placing  their  seed  there,  it  is  necessary  that,  vast  quantities  of  seed 
be  produced  each  year,  and  left  to  the  nlmiral  means  of  distri- 
bution.    In  this  way  plants  are  sending  out  seed  every  year  in  all 
directions,  so  that  it  may  be  ready  to  produce  new  plants  when- 
ever opportunity  offers. 

337.  Natural    means    for    distribution    of    plants. — The 
natural  means  for  the  distribution  of  plants  over  the  earth  is  a 
subject  of  great  interest  and  importance,  and  should  have  due 
consideration  in  the  study  of  plants.     While  studying  se^ds  and 
fruits  in  the  laboratory  especial  attention  should  be  given  to  those 
structures  and  peculiarities  which  assist  in  the  distribution  of  the 
seed.     In  excursions  to  the  fields,  forests,  or  parks,  instructive 

198 


SEED   DISPERSAL  199 

examples  are  often  met  with.  Most  plants  are  distributed  accord- 
ing to  natural  ways  by  means  of  seeds,  or  the  seedless  plants 
by  spores  (see  Chapters  XXIII-XXIX).  Some  seedless  plants, 
however,  are  distributed  also  by  buds  (Lycopodium  lucidulum, 
paragraph  514,  certain  ferns  as  Cystopterisbulbifera,  paragraph  496), 
and  some  by  plant  parts,  and  some  seed  plants  are  distributed  by 
other  means  than  by  seed.  The  best  means,  however,  for  natural 
distribution  of  the  seed  plants  is  by  the  seed.  There  are  several 
natural  means  by  which  the  seeds  are  dispersed,  the  most  impor- 
tant of  which  are  as  follows:  first,  by  the  wind;  second,  by 
animals;  third,  by  water;  fourth,  by  mechanisms  of  the  fruits  for 
the  forcible  expulsion  of  seeds. 

338.  Dispersal  of  seeds  by  the  wind. — Many  seeds  which  are 
small  and  light  are  often  blown  by  the  winds  for  considerable 
distances  without  having  any  special  provision  in  the  nature  of 
floats  or  wings.  The  seeds  of  many  grasses  and  other  herbs  are 
very  light  and  in  strong  gales  are  driven  far,  and  when  they  fall  on 
rather  hard  loose  ground  may  from  time  to  time  be  driven  along 
just  as  particles  of  soil  are.  There  are  many  seeds  or  fruits, 
however,  which  are  provided  with  special  appendages  which  serve 
as  floats,  or  as  surfaces,  which  "  catch  "  the  wind  and  enable  them 
to  be  borne  along.  Of  the  winged  seeds  notable  examples  are 
seen  in  the  samaras  of  the  elm,  where  a  thin  membranous  out- 
growth attached  to  the  seed  renders  the  seeds  buoyant,  or  the 
wing  is  firmer  as  in  the  blades  of  the  maple  or  pine.  In  the  milk- 
^veed  the  flattened  brown  seeds  a%  packed  in  great  numbers  and 
very  regularly  in  the  large  pods,  and  each  seed  has  a  large  tuft 
of  long,  white,  delicate,  hair-like  outgrowths.  These  hairs  are 
packed  very  closely  together  in  the  pod.  As  the  pods  split  open 
the  hairs  become  dry,  and  in  curling  take  up  much  more  room, 
thus  crowding  the  seeds  out  of  the  capsule,  when  they  are  caught 
by  the  wind  and  floated  away.  To  show  how  buoyant  they  are, 
such  seeds  may  be  set  free  in  the  quiet  air  of  a  room,  and  they  will 
float  slowly  to  the  floor.  In  the  Virginia  creeper,  or  virgin's 
bower,  the  long  curved  style  remains  attached  to  the  akene  and 
is  covered  with  numerous  delicate  bristles.  The  style  when  dry 


200  GROWTH   AND    WORK   OF   PLANTS 

is  more  or  less  spiral,  and  the  seeds  whirl  in  a  peculiar  fashion  as 
they  fly  through  the  air.  The  akene  which  contains  the  seed  is 
heavier  than  the  feathery  style,  and  as  it  falls  to  the  ground  the 
end  which  contains  the  radicle  ij  brought  next  the  ground,  so  that 
the  chance  of  germination  and  the  establishment  of  the  seedling  in 


Fig.  161. 
Dandelion  seeds. 

the  ground  is  favored.  Striking  examples  are  seen  in  the  "  seeds  " 
or  akenes  of  many  of  the  composite  flowers  like  the  dande- 
lion, thistle,  prickly  lettuce,  etc.  Here  the  hairy  pappus  on  the 
end  of  a  long  beak  provides  for  the  floating  of  the  fruit,  its  action 
being  much  like  that  of  a  parachute  as  the  akene  slowly  comes  to 


SEED   DISPERSAL 


201 


the  ground  "  right  side  up,"  i.e.,  with  the  radicle  of  the  embryo 
downward.  In  the  dandelion  the  flower  stem  elongates  just  as  the 
seed  is  ripening,  so 
that  the  head  is  lifted 
up  where  the  currents 
of  air  readily  reach 
it.  The  bristles  of 
the  pappus  in  many 
composites,  at  first 
straight,  turn  out  at 
nearly  right  angles, 
like  the  spokes  of  a 
tiny  wheel,  so  that  it 
is  more  effective  as  a 
float.  The  so-called 
"  tumble  weeds  "  are 
rolled  on  the  ground 
by  the  wind  to  great 
distances,  and  the 
seeds  are  scattered  by 
the  way.  Some  of 
these  are  the  light, 
much  branched 
grasses,  which  when 
ripe  and  dry  are 
broken  off  by  the  wind 
andsweptalongonthe 
ground.  The  "  res- 
urrection "  plant  (Ly- 
copodium)  is  another 
example  of  a  plant 
which  is  distributed 
by  the  wind.  As  it 
dries  up  during  droughts  it  curls  into  a  rounded  mass,  the  roots 
are  torn  from  the  ground,  it  rolls  along  in  the  wind,  and  with 
the  advent  of  rains  takes  root  and  grows  again. 


Fig.  162. 
Lactuca  scariola. 


202 


GROWTH   AND    WORK   OF   PLANTS 


339.  Dispersal  of  seeds  by  animals. — In  general  there  are  two 
ways  in  which  animals  distribute  seeds:  first,  by  eating  the  fruits; 

second,  by  seeds  which  cling  to  their 
bodies.  Edible  seeds  and  fruits.  In  the 
case  of  small  seeds  or  grains  which 
are  eaten  by  animals  not  all  the  seeds 
are  crushed  and  some  pass  through 
the  alimentary  canal  unharmed.  In 
the  case  of  fruits  eaten  by  animals 
many  have  small  seeds  with  hard  seed 
coats,  and  very  few  of  these  seeds  are 
crushed.  The  hard  seed  coats  further 
protect  the  embryo  from  the  solvent 
action  of  gastric  juices,  while  in  the 
case  of  some  seeds  it  is  believed  that 
they  germinate  better  after  being  sub- 
jected to  the  action  of  various  sub- 
Fig.  163.  stances  while  passing  through  the 

Fruit  of  burdock  (Arctium  lappa).       alimentary  canal  of  birdSj   etc        Fmits 

like  the  raspberries,  blackberries,  grapes,  cedars,  are  eaten  by 
birds  and  other  animals  and  the  seeds  de- 
posited often  far  away  from  the  place  where 
they  were  grown.  Many  such  fruits  have 
bright  colors  and  attractive  flavors  at  the 
time  of  ripening.  Grapplers  on  seeds  and 
fruits.  These  are  well  known  to  nearly  all 
persons  who  tramp  the  fields  or  forest,  and 
may  also  be  "  picked  up  "  along  the  high- 
ways and  in  gardens.  Hooks  or  barbs  are 
produced  on  parts  of  the  fruit  which  cling 
tenaciously  to  rough  soft  objects  coming  in 
contact  with  them.  Common  among  these 
are  the  "  beggar  ticks,"  the  akenes  of  one  of 
the  composites  (Bidens),  which  have  barbs  burdock- 
on  the  two  lateral  prongs  at  one  end  of  the  flattened  fruit. 
In  some  sections  these  are  called  "  devil's  bootjack."  Slender 


Fig.  164. 
Hooks  and  akene  of 


SEED   DISPERSAL 


203 


akenes  of  the  same  genus  are  called  "  Spanish  needles."  The 
oval  fruit  of  the  "  cockle-bur "  is  covered  with  long  hooks. 
In  the  "  burdock  "  the  numerous  bracts,  surrounding  the  head 
containing  the  numerous  akenes,  are  extended  into  a  long 
slender  process  terminating  in  a  hook.  The  "  sticktights,"  or 
"  tick  trefoil,"  are  sections  of  the  pod  of  a  leguminous  plant  (Des- 
modium  =  Meibomia)  which  are  covered  with  numerous  hooks. 
In  the  various  species  of  avens  (Geum)  the  long  style  of  the  akene 
is  jointed  near  the  end  and  curved  into  a  hook.  It  separates  at 
the  joint,  leaving  the  hook  on  the  long  beak  (fig.  167).  Besides 
the  seeds  provided  with 
grapplers  many  seeds  ad- 
here with  mud  to  the  feet 
of  animals,  and  in  the  case 
of  birds  are  often  trans- 
ported to  great  distances, 
especially  by  wading  birds 
and  waterfowl. 

340.  Dispersal  of  seeds 
by  water.— Streams  have 
long  been  recognized  as 
lines  for  the  transport  and 
centers  of  distribution  of 
seeds.  Some  seeds  because 
of  their  light  weight  and 
slightly  impervious  coats 
float  for  long  distances  on 
j  the  water.  Others  which 
may  sink  are  swept  along 
in  the  strong  current. 
Even  on  high  ground, 
many  seeds  are  carried  to 
considerable  distances  by 

the  "  run-off  "  water  during  heavy  rains.  Seeds  are  distributed  also 
along  the  shores  of  ponds  and  lakes  as  they  float  on  the  water 
which  is  moved  by  winds.  Also  along  the  shores  of  the  ocean  the 


t;ig-  165. 
Fruits  of  tick  trefoil  (Desmodium). 


204 


GROWTH  AND    WORK   OF  PLANTS 


seeds  of  many  coastal  plants  are  distributed  to  great  distances  by 
the  ocean  currents.     It  has  been  found  that  many  seeds  will 

retain  their  vitality  after  immer- 
sion in  the  salt  water  cf  the 
ocean  for  three  or  four  weeks, 
and  some  will  germinate  after 
prolonged  immersion.  Darwin 
has  shown  by  experiment  that 
about  fourteen  per  cent  of  the 
seeds  cf  British  plants  will  bear 
immersion  in  sea  water  for  four 
weeks  and  still  germinate.  The 
distribution  of  certain  plants  en 
near-by  islands,  or  in  some 
cases  on  islands  quite  remote, 
is  sometimes  explained  by  the 
ability  of  the  seeds  to  bear  the 
prolonged  soaking  of  an  ocean 
Flg-  l66-  voyage  from  one  shore  to 

Seed  pod   of  tick  trefoil    (Desmodium);    at          '    e 
the  right  some  of  the  hooks  greatly  magnified,     another. 


Fig.  167. 
Seeds  of  Geum  showing  the  hooklets  where  the  end  of  the  style  is  kneed. 


SEED    DISPERSAL 


205 


341.  Dispersal  of  seeds  by  expulsion. — The  seeds  of  many 
plants  are  thrown  for  short  distances  by  the  sudden  explosion  of 
the  capsules,  or  by  pressure  which  squeezes  them  out  in  such  a 
way  that  they  are  suddenly  released.  The  valves  of  the  pods  in 
the  common  vetch  (one  of  the  wild  peas),  as  they  dry,  are  brought 
into  a  spiral  tension  so  that  they  suddenly  split  apart  and  curl, 


Fig.  1 68. 

Touch-me-not  (Impatiens  fulva);  side  and  front  view  of  flower  below;  above  unopened 
pod,  and  opening  to  scatter  the  seed. 

thus  throwing  out  the  peas.  In  the  "  touch-me-not  "  (Impa- 
tiens) the  valves  of  the  pod  are  also  in  tension,  and  when  touched 
or  jarred  they  split  and  curl  with  sudden  force,  scattering  the 
seeds.  In  others,  as  in  the  witch  hazel  and  violet,  the  pod  splits 
open  and  the  valves  squeeze  from  behind  in  such  a  way  as  to 
force  the  seeds  out  in  much  the  same  manner  that  many  a  child 
shoots  watermelon  or  apple  seeds  by  squeezing  them  from  between 
the  thumb  and  finger.  The  "  squirting  cucumber  "  is  so  called 
because  by  the  absorption  of  water  a  pressure  is  produced  which 
squirts  out  the  seeds. 


PART  II. 

GENERAL  MORPHOLOGY  AND  CLASSIFICATION  OF 

PLANTS. 


CHAPTER  XXII. 

OUTLINE   OF  CLASSIFICATION. 

342.  Morphology*  of  plants^ is  the  study  of  the  forms  of 
plants  and  the  form  of  plant  parts.     In  the  study  of  the  life  and 
work  of  plants  we  have  studied  the  form  of  the  plant  parts  (of 
the  higher  plants)  in  their  relation  to  function,  i.e.,  in  relation 
to  the  work  which  they  perform.     A  more  critical  .and  minute 
study  of  the  plant  parts  would  be  necessary  in  connection  with  the 
special  classification  or  identification  of  plants,  as  for  example 
in  the  determination  of  the  flowers.     In  general  morphology  we 
study  the  more  general  types  of  form  under  which  the  plant  parts 
appear.     In  comparative  morphology  we  study  the  form  of  the 
same  organ  or  plant  part  in  different  plants,  even  in  those  of  very 
remote  relationship,  in  order  to  recognize  organs  of  the  same  kind 
under  different  guises,  and  to  trace  the  evolution  of  plant  organs 
in  order  to  acquire  a  clearer  knowledge  of  the  broader  relation 
ships  existing  among  all  plants. 

343.  Classification. — Classification    is    the    arrangement 
classifying  of  objects  or  ideas  in  an  orderly  and  intelligible  manner 
in  such  a  way  that  those  of  one  special  kind  or  general  kind  ar 
grouped  together.    The  classification  of  plants,  then,  is  the  arrange 
ment  of  plants  according  to  the  kinds,  or  according  to  the  rela 
tionships,  into  larger  or  smaller  groups  according  to  the  grade  o 
relationship  and  the  number  of  plants  of  any  one  kind.     Fo 

*  jjLop<f>^=  form,  \6yos  =  discourse. 
206 


PLANT  KINGDOM  2OQ 

work  will  permit  the  discussion  of  but  a  few.  It  may  be  con- 
venient to  precede  this  study  with  a  brief  outline  of  a  general 
classification  including  the  divisions  of  a  higher  grade,  since  it  is 
only  the  more  general  features  of  morphology  and  relationship 
which  come  within  the  scope  of  this  work. 


PLANT   KINGDOM. 

SUBKINGDOM  I.  Thallophyta. 

THE    ALG^. 

Class  I.    Chlorophycese. 

Subclass  Protococcoideae. 

Subclass  Conjugatae. 

Subclass  Confervoideae. 

Subclass  Siphoneae. 
Class  II.    Charophyceae. 
Class  III.    Cyanophyceae. 
Class  IV.   Diatpmeae;  or  BacillarialeSo 
Class  V.    Phaeophyceae. 
Class  VI.    Rhodophyceae. 

THE   SLIME   MOLDS. 

Class  VII.    Myxomycetes. 

THE    BACTERIA. 

Class  VIII.    Schizomycetes. 

THE    FUNGI. 

Class  IX.   Phycomycetes. 
Class  X.   Ascomycetes. 
Class  XL   Basidiomycetes. 


210  GENERAL   MORPHOLOGY   OF   PLANTS 

SUBKINGDOM  II.   Bryophyta. 

THE    LIVERWORTS. 

Class  XII.   Hepaticae. 

THE    HORNED    LIVERWORTSo 

Class  XIII.    Anthocerotes. 

THE    MOSSES. 

Class  XIV.    Muscineae. 
SUBKINGDOM  III.   Pteridophyta. 

THE    FERNS. 

Class  XV.   Filicineae. 

THE    HORSETAILS. 

Class  XVI.    Equisetineas. 

THE    CLUB    MOSSES. 

Class  XVII.    Lycopodineae. 

THE    QUILLWORTS. 

Class  XVIII.    Isoetineae. 
SUBKINGDOM  IV.   Spermatophyta. 

THE   NAKED    SEED    PLANTS. 

Class  XIX.    Gymnospermae. 

THE    ENCLOSED    SEED    PLANTS, 

Class  XX.   Angiospermae. 


CHAPTER   XXIII. 
ALGvE. 

347.  The  algae  are  plants  of  a  low  grade  of  organization. 

They  live  in  the  water,  or  a  few  of  them  in  moist  situations. 
Those  growing  in  the  sea  are  popularly  called  "  sea  mosses,"  while 
those  growing  in  fresh  water  are  called  "  pond  scums,"  "  water 
nets,"  etc.  It  should  be  understood  that  the  algae  are  not  true 
mosses.  They  are  all  simpler  in  structure  and  lower  in  the  scale  of 
classification  than  the  mosses.  The  simplest  algae  are  single-celled 
plants.  From  this  simple  condition  single  individuals  or  cells  are 
easily  associated  into  colonies,  or  firmly  united  into  filaments,  or 
cell  plates,  which  reach  massive  size  in  the  rockweeds  and  kelps. 

348.  The  plant  body  of  the  algae  thus  varies  greatly  in  size 
as  it  does  in  form.     The  plant  body  of  the  algae  is  not  divided 
into  true  stems,  roots,  and  leaves.    There  are,  it  is  true,  algae  which 
possess  root-like,  stem-like,  and  leaf -like  organs,  but  they  do  not 
belong  to  the  same  part  in  the  plant's  life  cycle  that  the  true  roots, 
stems,  and  leaves  of  the  ferns  and  seed  plants  do.     For  this  reason 
they  are  not  regarded  as  true  roots,  stems,  or  leaves  from  the 
standpoint  of  comparative  morphology,  although  from  the  stand- 
point of  physiology  or  function  such   algae   possess  stems  and 
leaves.     Such  a  plant  body,  which  is  not  differentiated  into  true 
roots,  shoots,  and  leaves,  is  called  a  thallus.    The  plant  body  of  the 
algae  as  well  as  of  the  fungi  is  a  thallus.     They  are  characteris- 
tically the  thallus  plants  or  Thallophytes. 

The  algae  possess  chlorophyll  *  and  are  thus  able  to  live  inde- 

*  There  are  a  few  parasitic  algae  which  lack  chlorophyll,  and  their 
method  of  nutrition  is  similar  to  that  of  the  fungi,  although  some  of  them 
store  starch  which  they  obtain  from  their  green  host.  Example,  Rhodochy- 
ttium,  parasitic  on  the  ragweed  in  North  Carolina,  and  probably  other 
Southern  and  Atlantic  States,  and  on  one  of  the  milkweeds  in  Kansas. 

211 


212 


GENERAL   MORPHOLOGY   OF   PLANTS 


pendently  of  other  plants.  They  obtain  their  mineral  and  nitrog- 
enous foods  from  the  water,  while  they  fix  the  carbon  from  the 
carbonic  acid  absorbed  from  the  water,  in  the  presence  of  the 
•chlorophyll  and  sunlight. 

The  characters  of  structure  and  reproduction  should  be  studied 
in  connection  with  the  individual  plants. 

GREEN   ALG.E*  (CHLOROPHYCE^E). 

The  Conjugating  Green  Algce  (Conjugates}. 

349.  Spirogyra. — The  plant  spirogyra  lives  in  fresh  water  in 
ponds,  the  borders  of  lakes,  or  in  pools. 
Sometimes  it  is  found  in  very  slow-running 
water.  It  is  in  the  form  of  simple  threads 
or  filaments  which  may  be  quite  long  and 
are  unbranched.  Large  numbers  of  these 
threads  are  tangled  together  into  a  mat 
which  floats  in  the  water.  Much  gas  which 
is  given  off  during  photosynthesis  is  caught 
in  the  meshes  of  the  tangle,  buoys  the  mat 
of  the  alga  up  to  the  surface  of  the  water 
where  the  light  is  more  efficient,  and  gives 
the  plant  a  frothy  appearance,  which  sug- 
gested such  names  as  "  pond  scum,"  "  frog 
spittle,"  etc.  The  threads  are  made  up  of 
cells  which  are  cylindrical  in  form  and 

Fig.  169.          Fig.  170.  *  To  THE  TEACHER.     The    number  of  green 

Spirogyra   .     Spirogyra      j        studied  must  be  determined  by  the  teacher, 
before     plac-    in  5  per  cent     a  o  ' 

ing  in  salt  salt  solution.    and  will  depend  to  some  extent  on  the  time,  the 

facilities,  and   material    at   hand.     If  only  one  is 

studied  carefully  it  preferably  should  be  Spirogyra.  If  two,  then  Vaucheria 
or  (Edogonium  should  be  included  because  of  the  differentiation  of  the  sex 
organs.  In  more  advanced  classes  the  shield  Coleochaete  might  be  included. 
In  addition  to  laboratory  work,  such  portion  of  the  text  should  be  studied* 
as  the  teacher  finds  time  and  adaptability  of  the  pupils  will  permit.  The 
general  features  of  the  plant  body,  the  progression  from  single  cells  to  threads 
and  cell  plates,  the  general  features  of  sex  organs  and  their  differentiation 
into  two  kinds,  as  well  as  the  life  cycle,  should  always  be  kept  foremost. 


GREEN  ALGM  21 3 

joined  end  to  end.     These  threads  are  delicate  and  silky  in  appear- 
ance and  somewhat  slimy  to  the  touch  when  lifted  by  the  hand. 

350.  The  spirogyra  cell.* — The  thread  of  spirogyra  is  com- 
posed of  similar  cells,  and  a  study  of  one  cell  is  sufficient  to  show 
the  structure  of  all  in  the  vegetative  or  growing  stage.  The  most 
prominent  part  of  the  cell  is  the  chlorophyll  body,  which  is  in  the 
form  of  a  spiral  band  and  lies  next  the  inside  of  the  cell  wall 
coiled  around  in  the  cell.  The  band  is  more  or  less  irregular 
along  the  edges.  The  number  of  these  chlorophyll  bands  in  a  cell 
varies  in  the  different  species  from  one  to  five  or  six,  while  in  a 
given  species  the  number  may  vary  from  one  to  two,  in  another 
from  two  to  three,  and  so  on.  At  quite  regular  intervals  in  the 
chlorophyll  band  there  is  a  round  shining  nodule-like  body  called 
a  'pyrenoid.  The  pyrenoid  is  peculiar  to  the  algae,  being  found  in 
many  of  them.  Outside  of  the  algae  it  is  found  only  in  a  few 
species  of  liverworts.  The  pyrenoids  are  probably  reserve  food 
products  of  a  proteid  nature.  The  pyrenoid  in  spirogyra  is  often 
surrounded  by  a  layer  of  fine  starch  grains. " }  Near  the  center  of 
the  cell  is  a  large  body  of  a  more  or  less  granular  nature  and  color- 
less. This  is  the  nucleus  of  the  cell.  It  is  elliptical  to  convex  in 
form  or  in  outline  as  seen  in  profile  in  some  species,  and  angular  in 
others.  Within  each  nucleus  is  a  nucleolus  (sometimes  two  or 
three  nucleoli).  In  the  living  cell  these  usually  appear  more 
dense  than  the  substance  of  the  nucleus  and  highly  refringeat. 
The  protoplasm  of  the  cell  is  a  viscid  granular  substance  forming 
a  thin  layer  next  the  wall  which  is  connected  by  strands  of  the 
same  substance  which  radiate  out  from  a  granular  layer  surround- 
ing the  nucleus.  These  strands  can  be  distinctly  seen,  as  they 
radiate  out  from  the  angles  of  the  nucleus,  and  divide  into  more 
slender  strands  which  terminate  in  the  wall  layer  of  protoplasm 
at  a  point  where  the  pyrenoid  is  located  in  the  band.  The  spaces 
between  the  strands,  which  here  are  quite  large,  are  filled  with  a 
watery  fluid,  the  cell  sap.  The  term  protoplasm  was  earlier  used 
to  include  the  nucleus,  which  was  supposed  to  be  only  a  denser 

*  This  paragraph  is  chiefly  for  reference,  but  advanced  classes  may  be 
able  to  include  it. 


2I4 


GENERAL   MORPHOLOGY   OF   PLANTS 


Protoplasm 
in  old  sense 


Cytoplasm 


[ectoplasm 


portion  of  it.  Now  the  nucleus  is  known  to  be  a  distinct  organ 
of  the  cell,  while  the  protoplasm  proper  is  called  the  cytoplasm,  i.e., 
the  cell  plasm.  Strictly  speaking  the  cytoplasm  shows  two  dif- 
ferent conditions  or  kinds,  a  very  thin  outer  layer  next  the  wall, 
which  is  homogeneous,  the  ectoplasm,  and  the  inner  portion,  of  a 
granular  nature,  the  endoplasm.  The  structure  of  the  cell  of 
spirogyra  might  be  recapitulated  as  follows: 

wall 
Chlorophyll  band 

or 

Chloroplast 

Cell   \     Sphere  of  starch  grains 
Pyrenoid 

jendoplasm 
Wall  layer 
Nuclear  layer 
Strands 

Nucleus  and  nucleolus 
Vacuoles  containing  cell  sap 

351.  The  structure  of  the  spirogyra  cell  represents  funda- 
mentally the  structure  of  all  living  cells  in  the  resting  condition, 
i.e.,  when  the  cell  is  not  dividing.     The  chlorophyll  is  absent  in 
many  cells,  and  so  are  the  pyrenoid  and  starch  grains.     But  the 
cytoplasm,  the  vacuoles,  the  nucleus  and  nucleolus  are  present 
in  all  living  cells.     The  cytoplasm,  nucleus  and  nucleolus  con- 
stitute the  living  substance  of  the  cell.     By  reference  to  fig.  171 
of  the  amoeba,  a  single-celled  animal,  these  important  parts  of  the 
cell  are  seen  to  be  present. 

352.  Plasmolysis  of  the  cell.*  — The  plant  spirogyra  is  an 
excellent  one  in  which  to  study  certain  work  of  the  cell.     In  the 

*  This  subject  might  well  be  introduced  in  connection  with  the  study 
of  methods  for  strengthening  the  stem  and  leaves  or  in  the  study  of  ab- 
sorption by  roots.  It  is  introduced  here  for  the  reason  that  spirogyra  is 
much  easier  to  use  than  the  tissues  of  the  higher  plants  because  no  sections 
are  necessary.  Also  it  is  convenient  in  connection  with  the  study  of  spiro- 
gyra as  a  plant.  The  paragraph  is  chiefly  for  reference. 


GREEN   ALGM 


215 


normal  condition  of  working  cells  they  are  in  a  condition  of 
turgor,  that  is,  they  are  in  a  state  of  tension  produced  by  inside 
pressure.  This  makes  the  cell  plump,  as  one  might  say,  or  firm. 
When  cells  are  united  together  in  masses  as  in  vegetables,  in 
leaves,  or  in  succulent  stems,  all  of  the  cells  being  in  a  state  of 
turgor,  these  parts  of  ^ 

the  plant  are  firm  and 
held  in  position.  If 
the  cells  lose  their  tur- 
gor the  tissues  become 
limp  or  wilted.  The 
inside  pressure  (or  en-  • 
dosmotic  pressure)  is 
due  to  the  presence  of 
certain  salts,  sugars, 
etc.,  in  the  cell  sap 
which  are  separated'  // 

from  the  water  outside 
of  the  cell  by  the  cell  '  Fig.  171. 

n          1,1  11  i  Amoeba,   showing  pseudopodia.  —  Ect.  ectoplasm,   End. 

Wall  and  the  Wall  layer     endoplasm,    N.    nucleus,    Pv.    pulsating  vacuole.     (After 

or  membrane  of  proto- 
plasm (or  more  strictly  speaking  by  the  ectoplasm).  Since  the 
water  outside  has  no  salts  in  it,  or  if  present  they  are  in  a  less 
concentrated  form  than  those  in  the  cell  sap,  the  water  moves 
more  readily  through  the  plasma  membrane  into  the  cell  sap  than 
it  can  move  outward.  The  inside  pressure  presses  the  plasma 
membrane  firmly  against  the  cell  walls.  The  cell  wall  being 
elastic,  yields  slightly  and  thus  is  pressing  in  the  opposite  direction 
against  the  plasma  membrane.  This  produces  the  state  of  turgor 
in  the  cell.  The  opposite  condition  of  turgor  in  the  cell  is  plas- 
molysis,  or  shrinking  of  the  plasm.  This  can  be  produced  arti- 
ficially by  mounting  some  threads  of  spirogyra  in  a  five  per  cent 
solution  of  common  table  salt,  or  in  a  strong  sugar  solution. 
This  solution  being  of  a  greater  concentration  than  that  of  the 
cell  sap,  the  .flow  of^the  water  is  now  m_the  outward  direction 
through  the  plasma  membrane,  and  this  is  pressed  inward  from 


216 


GENERAL   MORPHOLOGY   OF  PLANTS 


the  cell  wall,  as  shown  in  fig.  170.  It  often  takes  place  so  regu- 
larly that  the  contents  of  the  cell  are  collected  into  a  well-defined 
sphere  or  elliptical  body  inside  the  cell.  Now  if  the  salt  solution 
be  removed  and  fresh  water  added,  the  movement  of  water  will 
be  inward  again,  the  cell  will  recover  from  the  state  of  plasmolysis 
and  be  restored  to  the  state  of  turgor. 

353.  The  growth  and  multiplication  of  spirogyra. — The 
thread  of  spirogyra  grows  by  the 
division  of  cells  and  then  elongation 
of  the  cells.  The  nucleus  divides  first 
into  two  nuclei  and  a  cross  wall  is 
then  laid  down  between  them.  The 
two  daughter  cells  are  at  first  shorter 
than  the  parent  cell,  but  each  one 
soon  elongates.  This  process  taking 
place  in  all  of  the  cells  brings  about 
the  rapid  elongation  of  the  thread. 
Multiplication  of  the  threads  takes 
place  by  the  separation  of  a  single 
thread  into  several  shorter  ones,  the 
thread  breaking  at  a  cross  wall,  by 
the  splitting  of  the  cross  wall,  so  that 
the  cell  is  not  injured.  Strong  inside 
pressure,  which  sometimes  results  by 
a  change  in  the  water,  often  causes 
this  separation  of  the  threads. 

354.  Reproduction  by  conjuga- 
tion.— Sexual  reproduction  in  spiro- 
gyra takes  place  by  a  process  known 
as  conjugation.  When  the  conditions 
are  favorable  two  threads  lying  near 
each  other  conjugate  by  tubes  devel- 
oped from  opposite  cells.  The  tubes 
meet  and  the  walls  at  the  point  of 
contact  dissolve,  making  an  open 
communication  between  the  two  cells.  This  is  the  conjugation 


U  _ 


Fig.  172. 
Zygospores  of  spirogyra. 


GREEN   ALG& 


217 


tube,   and  where  two  conjugating  threads  lie  side  by  side  for 

some  distance  the  conjugation  of  the   opposite  cells  presents  a 

ladder-like  figure.     The  protoplasm  from  one  of  the  cells  flows 

over  through  the  tube  into   the  cell  opposite,        -=^ 

carrying  with  it  the  chlorophyll  band  and  all  of 

the  cell  contents,  but  some  of  the  water  is  lost 

The    merged   contents   of   the    two   cells   now 

contract  into  a  rounded  or  elliptical  body  called 

the  zygospore,  or  zygote,  as  shown  in  fig.   172. 

A  thick  and  firm  wall  is  formed  and  much  of 

the  protoplasm  is  changed  into   an  oily   sub- 

stance,  in  which  condition  it  is  more  resistant 

to  unfavorable  conditions  of  dryness  or  cold. 

The  two  nuclei  fuse   into  one   nucleus.      The 

fusion  of  the  cell  contents  and  fusion  of   the 

nucleus  of  the  two  gametes  into  one  is  known 

as  fertilization.      The    zygospore    is   a   resting 

spore  and  serves  to  carry  the  plant  over  unfa- 

vorable conditions  or  periods  of  weather. 

355.  The  gametes  and  gametangia.  —  The 
cell  in  which  the  zygospore  is  formed  is  the 
receiving  cell,  while  the  other  one  is  the  supply- 
ing cell.  Each  conjugating  cell  is  a  gametangium 
(i.e.,  a  gamete  case),  and  the  portion  of  its 
content  which  takes  part  in  the  formation  of  the 
zygospore  is  a  gamete.  When  one  cell  of  a  thread 
in  ladder-like  conjugation  is  a  receiving  gamete, 
all  the  others  of  the  same  thread  are  also  receiv- 
ing gametes.  All  the  cells  of  a  single  thread 
are  likewise  supplying  gametes.  Usually  there 
is  no  difference  in  the  size  of  the  supplying  and 
receiving  cells,  and  it  is  impossible  to  say  what 
the  nature  of  the  gamete  is  until  movement  lt 
of  the  protoplasm  from  the  supplying  gamete  is  taking  place. 
While  the  sex  of  the  threads  appears  in  these  cases  to  be 
distinct,  there  is  no  differentiation  in  the  size  and  form  of  the  egg 


Fig.  173- 


°samc 


2l8  GENERAL   MORPHOLOGY   OF   PLANTS 

and  sperm,  the  receiving  gamete  corresponding  to  the  egg  or 
female  cell,  while  the  supplying  gamete  corresponds  to  the  sperm 
or  male  cell.  There  are  some  species,  however,  in  which  adja- 
cent cells  in  the  same  thread  conjugate  by  lateral  tubes  at  the 
adjacent  ends  which  bend  toward  each  other  and  fuse  in  the 
form  of  a  buckle  joint  (fig.  173).  Evidently  here  the  two  sex  ele- 
ments are  present  in  a  single  thread.  These  species  may  also 
conjugate  in  a  ladder-like  manner. 

356.  Germination  of    the   zygospore. — After  a  period  of 
rest  and  when  the  conditions  become  favorable  the  zygospore 
germinates  and  a  new  thread  is  developed  from  the  fertilized  egg. 

357.  Life   history   of    spirogyra. — The  .  life    history    of    a 
plant  is  an  account  of  its  development  from  the  egg,  or  from  some 
starting  point,  through  its  different  forms,  including  the  means  for 
propagation  and  reproduction,  until  the  egg,  or  the  same  starting 
point,  'is  reached  again.     The  life  history  of  spirogyra  may  be 
epitomized  as  follows.     The  zygospore  (the  fertilized  egg)  ger- 
minates and  produces  the  plant  in  its  filamentous  form,  the  vege- 
tative phase.     Growth  and  increase  take  place  by  division  and 
elongation  of  any  or  all  of  the  cells.     Propagation  or  multiplica- 
tion takes  place  by  the  breaking  up  of  the  threads  into  separate 
threads.     Sexual  reproduction  takes  place  by  conjugation,  either 
by  conjugating  tubes  betwreen  cells  of  two  distinct  threads,  or  by  a 
tube  forming  a  buckle  joint  connecting  two  adjacent  cells  of  the 
same  thread.     The  zygospore  is  formed  in  one  of  the  two  con- 
jugating cells  by  the  fusion  of  the  contents  of  the  two  cells  into  one, 
the  shrinkage  of  this  mass  from  the  wall  forming  a  rounded  body 
with  a  thick  wall  within  the  female  gamete  case,  or  egg  case. 
The  fusion  of  the  two  nuclei  in  the  zygospore  completes  the  proc- 
ess of  fertilization  of  the  egg  which  passes  through  a  resting  stage. 
The  life  history  is  sometimes  spoken  of  as  a  life  cycle.     It  may  be 
represented  by  the  diagram  or  by  the  following  formula:  * 

Plant,  veg.  ^ .  \  zygospore  =  fertilized  egg  — >  Plant,  etc. 

\  female  gamete  '. 

*  This  formula,  and  those  which  follow  other  groups  of  plants,  are  not  to  be 
memorized  by  the  pupil.  It  is  simply  presented  to  serve  as  a  graphic  repre- 
sentation of  the  life  cycle. 


GREEN   ALGM  2IQ 

This  formula  may  be  abbreviated  by  the  use  of  signs  as  follows : 
P  —  P  —  P  —   (  g  >  E  -»  P,  etc.,  in  which  P  stands  for  plant 

and  its  repetition  indicates  multiplication  of  the  plant  from  simi- 
lar parts,  not  by  means  of  special  reproductive  or  propagative 
bodies;  g  =  gamete,  E  =  the  fertilized  egg,  zygospore  or  oospore, 
as  it  is  called  in  special  cases. 

Sporophyte 


-      ^termination. 
Egg^NT- 


Diagram  No.  I.  Illustrating  the  life  cycle  in  the  development  of  Spirogyra.  Course 
of  development  follows  the  direction  indicated  by  arrows.  Zygote  equals  fertilized  egg, 
which  in  this  case  is  the  zygospore. 

358.  Zygnema. — Zygnema   is   another  genus  of  filamentous 
algae  closely  related  to  Spirogyra.     It  differs  chiefly  in  the  form 
of   the   chlorophyll  bodies.     These   are  star-shaped  and  two  in 
a   single    cell.     The    nucleus  in  the  cell  is  not  so  conspicuous. 
Growth,  multiplication  and  conjugation  take  place  as  in  Spiro- 
gyra.    The  life  history  follows  the  same  course  and  the  plant  is 
found  under  similar  conditions. 

359.  The   desmids. — The   desmids  form   another  family  of 
conjugating   algae.     They  are  mostly  single-celled  plants  of  very 
beautiful  form  and  markings,  while  a  few  of  them  unite  into 
filaments.     They  occur  in  fresh  water,  often  mingled  with  spiro- 
gyra  and  other  green  algae.     The  single-celled  forms  are  bisym- 
metrical,  each  half  being  exactly  like  the  other.     They  multiply 
by  dividing  so  as  to  separate  these  two  halves,  and  each  half  then 
reproduces  a  new  one  in  place  of  the  lost  half.     They  conjugate 
by  the  protoplasts  (the  cell  content)  from  two  cells  separating 
from  the  cell  wall  and  uniting  to  form  a  zygospore  which  is  thick- 
walled  and  often  beautifully  sculptured. 


220 


GENERAL  MORPHOLOGY   OF  PLANTS 


SINGLE-CELLED    GREEN    ALG^   (PROTOCOCCOIDEyE). 

360.  Pleurococcus.* — This  plant  is  a  representative  of  the 
single-celled  green  algae.     It  is  often  found  growing  on  the  north 
or  shaded  side  of  trees,  rocks,  walls,  etc.,  forming  a  thin  green 
layer.     The  green  mass  is  made  up  of  numerous  green  cells, 
single  or  in  groups  of  two,  three,  or  four.     These  groups  are 
formed   by  the  division  of   the    single  cells,  the    new  cells,  or 
"  daughter  "  cells,  remaining  attached  for  a  time  before  separat- 
ing.    Sexual  reproduction  is  not  known. 

361.  The  red  snow  plant,  Haematococcus. — This  is  a  single- 
celled  plant  which,  in  certain  stages  of  development,  contains  a 


Fig.  174. 

Sphaerella  lacustris  (Girod.)  Wittrock.  A,  mature  free-swimming  individual  with  central 
red  spot.  B,  division  of  mother  individual  to  form  two.  C,  division  of  a  red  one  to  form  four. 
D,  division  into  eight.  E,  a  typical  resting  cell,  red.  F,  same  beginning  to  divide.  G,  one 
of  four  daughter  zoospores  after  swimming  around  for  a  time  losing  its  red  color  and  be- 
coming green.  (After  Hazen.) 

red  pigment  which  disguises  the  color  of  the  chloroplast.  It  is 
often  found  covering  large  tracts  of  snow  in  arctic  regions.  A 
very  closely  related  species,  if  not  the  same,  inhabits  the  shores 
of  lakes,  ponds,  and  streams  in  rocky  areas  of  the  North  Tem- 
perate region.  It  is  often  found  in  shallow  depressions  of  rock 
along  the  shore,  where  in  dry  weather  it  resembles  a  coat  of  dull 
red  paint  on  the  rocks.  The  plant  is  now  in  the  resting  stage. 
When  rains  come  the  plants  revive,  come  out  of  the  resting  state, 
are  provided  with  two  long  lashes  or  whips  (cilia  or  flagella) 
*  Pleurococcus  vulgaris  =  Protococcus  vulgaris. 


FILAMENTOUS   GREEN   ALG& 


221 


which  lash  about  and  cause  the  plant  to  swim  rapidly  around  in 
the  water.  In  the  swimming  stage  the  plant  is  green,  the  chloro- 
phyll usually  not  being  obscured  by  the  red  pigment.  As  the  small 
pools  dry  out  the  swimming  plant  passes  again  into  the  resting 
stage  and  acquires  the  red  pigment. 

362.  Single-celled  green  algae  in  colonies. — The  single- 
celled  algae  just  described  lead  an  independent  or  individual 
existence.  There  are  others  in 
which  the  individuals  are  asso- 
ciated in  definite  colonies.  Some 
of  these  are  motile  during  their 
vegetative  existence  as  in  Pan- 
dorina  morum.  This  is  a  colony 
of  sixteen  like  individuals  ar- 
ranged in  the  form  of  a  sphere 
enclosed  in  a  thin  gelatinous 
sheath,  each  oval  individual 
with  a  pair  of  cilia  projecting 
beyond  the  sheath.  The  vibra- 
tion of  the  cilia  causes  a  rapid 
rotary  motion  of  the  sphere.  The 
colony  multiplies  by  each  in- 


Fig.  175- 

Pandorina  morum  (Mull.)  Bory.  I,  motile 
colony;  II,  colony  divided  into  16  daughter 
dividual     dividing      into       Sixteen    colonies;  III,  sexual  colony,  gametes  escap- 
„....,.  ,_.  ing;   IV,    V,   conjugating  gametes;  VI,  VII, 

Small     individuals.         The      Small     young  and  old  zygospore;    VIII,  zygospore 
.       .  .  forming  a  large  swarm  spore,  which  is  free  in 

COlomeS  Separate  from  the  parent    IX;  X,  same  large  swarm  spore  divided  to 
*    .  .  form  young  colony.     (After  Pringsheim.) 

and   grow    to   the    normal    size. 

Sexual  reproduction  takes  place  when  these  small  individuals 
separate  and  conjugate  in  pairs,  usually  a  small  one  with  a  large 
one,  producing  a  zygospore.  Some  of  the  colony  algae  are  non- 
motile  as  in  the  water-net  (Hydrodictyon). 


FILAMENTOUS  GREEN 

The  Confervas  (Confervoidea). 

363.  General  characters. — The  larger  number  of  these  algae 
are  thread-like,  either  simple  or  branched.  Some  of  the  marine 
forms  are  leaf -like,  as  the  "  sea  lettuce."  The  chlorophyll  is 


222 


GENERAL    MORPHOLOGY   OF   PLANTS 


in  small,  oval,  flattened  chloroplasts.  They  multiply  by  the  for- 
mation of  special  bodies  from  the  protoplasm  of  individual  cells. 
These  bodies  are  called  spores,  and  are  provided  with  cilia  so 
that  they  swim  about  in  the  water  after  escaping  from  the  parent 
cell.  They  are  thus  called  "  swimming  spores"  "  zoospores  " 
or  "  zoogonidia"  These  spores  are  not  formed  as  the  result 
of  a  sexual  process.  The  process  is  an  asexual  one,  hence 
they  are  often  termed  asexual  swimming  spores.  Sexual  repro- 
duction takes  place  in  some  by  the  fusion  of  two  swimming 
spores,  similar  to  the  asexual  spores,  forming  a  zygospore.  In 
others  definite  sexual  organs  are  formed,  a  large  one,  the  female 
organ,  an  egg  case  (called  an  oogonium),  which  contains  the  egg  or 
ob'spore;  and  a  smaller  one,  the  male  organ,  a  sperm  case  (called  an 
anlheridium),  containing  a  number  of  small  motile  male  cells,  the 
sperms.  Fertilization  in  these  results  from  a  fusion  of  a  sperm  with 
the  nucleus  of  the  egg. 

364.   Ulothrix. — Ulothrix  is  an  example  of  the  first  kind  of 
sexual  reproduction  described  above.     The  plant  forms  simple 

threads.  In  asexual  re- 
production a  number  of 
small,  oval,  4-ciliated  swim- 
ming spores  are  formed 
from  the  protoplasm  of  a 
single  cell.  These  escape, 
and  after  the  swimming 
period  come  to  rest,  ger- 
minate and  produce  the 
Ulothrix  thread  again.  In 
sexual  reproduction  similar 
biciliate  swimming  spores 
are  formed  which  unite  in 
pairs  to  form  zygospores 
(fig.  176).  Cladophora, 
Chcetophora,  Drapernau- 
with  a  similar  method  of 


c 


Fig.  176. 

Ulothrix  zonata.  A,  base  of  thread.  B,  cells  with 
zoospores,  C,  one  cell  with  zoospores  escaping  another 
cell  with  small  biciliate  gametes  escaping  and  some 
fusing  to  form  zygospores;  E,  zoospores  germinating 
and  forming  threads;  F,  G,  zygosoore  growing  and 
forming  zoospores.  (After  Caldwell  and  Dodel.) 


dia,    etc.,    are 
reproduction. 


branched    forms 


FILAMENTOUS   GREEN   ALGJE 


223 


365.  CEdogonium. — (Edogonium  is  an  example  of  the  second 
kind  of  sexual  reproduction.  The  thread-like  plant  is  simple. 
It  grows  in  length  by  the  repeated  division  of  certain  cells,  the 
marks  of  the  successive  divisions  remaining  on  the  cell  wall  near 


Fig.  177. 

Portion  of  thread  of 
oedogonium,  showing 
chlorophyll  grains,  and 
peculiar  cap  cell  walls. 


Fig.  178. 

Zoogonidia  of  CEdogonium  escaping. 
At  the  right  one  is  germinating  and 
forming  the  holdfasts,  by  means  of 
which  these  algas  attach  themselves 
to  objects  for  support.  (After  Prings- 
heim.) 


Fig.  179. 

CEdogonium  undulatum,  with 
oogonia  and  dwarf  males;  the  up- 
per oogonium  at  the  right  has  a 
mature  oospore. 


one  end,  giving  a  peculiar  appearance  as  in  fig.  177.  In  asexual 
reproduction  the  content  of  a  cell  forms  a  single  large  zoospore  or 
swimming  spore,  with  a  crown  of  cilia  near  one  end.  After 
escaping  from  the  parent  cell  and  swimming  around  it  comes  to 


224  GENERAL   MORPHOLOGY   OF  PLANTS 

rest,  attaches  itself  to  a  place  of  support  by  a  disk-like  grappler, 
and  grows  into  another  (Edogonium  thread.  In  sexual  repro- 
duction certain  cells  become  transformed  into  female  organs  by 
becoming  enlarged  and  rounded.  This  enlarged  cell  is  the  egg 
case  (oifgenium,  or  egg  producer),  and  contains  a  single  large 
egg  or  oospore.  Other  cells  become  divided  into  smaller  cells 
by  cross  walls.  Each  of  these  small  cells  is  a  male  organ,  the 
sperm  case  (antheridium).  The  sperms  are  like  the  swimming 
spores,  but  much  smaller  and  devoid  of  chlorophyll.  One  enters 
an  egg  case,  passes  into  the  egg  and  unites  writh  the  nucleus. 
The  fertilized  egg  (oospore)  then  acquires  a  thick  wall  and 
becomes  a  resting  spore.  After  a  period  of  rest  the  proto- 
plasm of  the  fertilized  egg  forms  four  zoospores,  each  of 
which  can  grow  into  an  (Edogonium  plant,  thus  completing 
the  life  cycle.  In  some  species  both  the  sperm  case  and  egg 
case  are  on  the  same  thread,  while  in  other  species  they  aie 
on  separate  threads.  In  still  others  small  male  plants  are 
first  formed  from  a  special  swimming  spore  intermediate  in 
size  and  color  between  a  zoospore  and  sperm. 

Sporophyte 

Zygote  n~T)  Mother  cell 
Sperm 

Antxwgon. 


Diagram  No.  II.  Illustrating  the  life  cycle  in  the  development  of  (Edogonium.  Course 
of  development  follows  the  direction  indicated  by  arrows.  Zygote  equals  fertilized  egg. 
Asexual  multiplication  by  asexual  spores.  ^ 

366.  Coleochaete. — Coleoch&te  .represents  the  highest  stage 
of  development  of  the  filamentous  green  algae.  The  plants 
occur  in  Afresh  water  attached  to  larger  aquatic  plants.  They 
are  mostly  filamentous  and  branched,  but  a  few  form  small, 


FILAMENTOUS   GREEN   ALG& 


22$ 


o    i! 


Fig.  1 80. 

Stem  of 
aquatic  plant, 
showing  Co- 
1  eoc  h  ae  te  , 
natural  size. 


Fig.  181. 
Thallus  of  Coleochaete  scutata. 


flattened,  more  or  less  circular  cell  plates.  Asexual  repro- 
duction is  by  biciliate  zoospores,  one  each  from  a  parent  cell. 
In  sexual  reproduction  sperm 
cases  are  formed  in  groups 
of  four,  each  one  producing 
a  small  biciliate  sperm.  The 
egg  cases  (oogonia)  are  large 
and  possess  a  long  slender 
beak  called  a  trichogyne. 
The  sperm  becomes  attached 
to  the  trichogyne;  its  nu-  Fig.  182. 


Fig.  183. 

Portion   of    thallus 
of      Co  1  eoc  haete 

Portion  of  thallus  of   Co-  scutata,       showing 
cleUS         moves        down       the     leochaete    scutata,    showing   four      antheridit 

empty    cells     from     which   formed      from      one 
zoospores      have     escaped,   thallus     cell;     a   sin- 
one    from    each    cell;    zoo-  gle  sperm  at  the  right, 
spores    at  the   left.     (After  (After  Pringsheim.) 
eim.) 


tube,  enters  the  egg  and 
fuses  with  the  nucleus  of 
the  egg.  The  egg  after  fer- 
tilization becomes  surrounded  by  an  envelope  of  branches  growing 
from  cells  adjacent  to  the  egg  case,  and  then  passes  through  a 
resting^stage.  When  it  germinates  it  produces  a  small  mass  of 


220 


GENERAL   MORPHOLOGY   OF   PLANTS 


cells,  each  of  which  forms    a   zoospore    capable   of   producing 
the  Coleoch&te  plant  again. 


^^s    ,«r^Cr 


Fig.  184.  Fig.  185. 

Two  sporocarps  still  Sporocarp  ruptured  by 
surrounded  by  thallus.  growth  of  egg  to  form  ceil 
Thallus  finally  decays  and  mass.  Cells  of  this  sporo- 
sets  sporocarp  free.  phyte  forming  zoospores. 

'  Figs.  184,  185.    C.  scutata.  , 

SIPHON   GREEN   ALG^   (SIPHONED). 

367.  General   characters. — The    siphon    algae    are    mostly 
filamentous  and  branched,  but  are  characterized  by  the  absence 
of  cross  walls  in  the  vegetative  threads,  or  by  few  such  walls. 
The  threads  are  thus  like  a  siphon  or  tube.     There  are  many 
nuclei. in  the  protoplasm  of  a  single  thread  or  compartment.     The 
chlorophyll  bodies  are  numerous,  small,  oval,   flattened  bodies. 
Asexual  reproduction  is  by  zoospores,  or  in  some  cases  by  non- 
motile  spores.     Sexual  reproduction  is  either  by  the  conjugation 
of  small  motile  gametes,  or  by  the  special  organs,  the  sperm  and 
egg  cases  (antheridia  and  oogonia). 

368.  The  green  felts  (Vaucheria). — The  "  green  felts  "  are 
good  examples  of  the  siphon  algae.     They  occur  in  fresh-water 


Fig.  186. 
Vaucheria  sessilis,  one  antheridium  between  two  oogonia. 


SIPHON   GREEN   ALG& 


227 


ponds,  lakes,  streams,  or  on  damp  soil.  The  threads  are  long, 
branched,  and  continuous,  that  is  without  cross  walls  except  where 
reproductive  organs  or  cells  "  i  \ 

are     formed.      The     plants  /    ' 

usually  form  dense  mats  of 
a  coarse  consistency  and  are 
known  as  "green  felts,"  be- 
cause of  the  felted  consist- 
ency of  the  mats.  Asexual  F>g- l8?- 

,  v          ,  Vaucheria  sessilis;  oogonium    opening    and 

reproduction      IS       Dy      large         emitting  a  bit  of  protoplasm;   sperms;   sperms 

e  ,    e  .1  entering    oogonium.      (After   Pringsheim   and 

spores  formed  from  the  pro-       Goebei.) 

toplasm  in  the  ends  of  the  threads  separated  by  a  cross  wall. 


Fig.  188. 

Fertilization  in  Vaucheria.     mn,  male  nucleus;  fn,  female  nucleus.     Male  nucleus  entering 
the  egg  and  approaching  the  female  nucleus.     (After  Oltmanns.) 

Some  of  these  spores  are  motile,  \vith  numerous  pairs  of  cilia  over 
the  surface,  while  others  are  non-motile.    These  spores  escape  from 


In 


, 

I^B>1 


Fig.  189. 

Fertilization  of  Vaucheria.   fn,  female  nucleus;  mn,  male  nucleus.     The  different  figures 
show  various  stages  in  the  fusion  of  the  nuclei. 

the  enclosing  cell  wall.     In  sexual  reproduction  specialized  short 
branches  are  formed,  which  are  separated  from  the  parent  wall 


228  GENERAL   MORPHOLOGY   OF  PLANTS 

by  cross  walls.  Some  of  these  become  broadly  oval  and  form 
the  egg  cases  (oogonia),  each  with  a  single  egg.  Others  are 
slender  and  more  or  less  curved.  These  are  the  sperm  cases 
(antheridia),  and  contain  numerous  biciliate  sperms.  In  fertili- 
zation a  sperm  enters  the  egg  case  at  the  opened  end,  passes  into 
the  egg  and  unites  with  one  nucleus  at  the  center.  A  thick-walled 
resting  spore  is  now  formed,  the  oospore,  which  in  turn  germinates 
and  produces  the  green-felt  plant  again. 


STONEWORTS,   OR  BASS  WEEDS   (CHAROPHYCE^E). 

369.  General  characters. — The  stoneworts  or  bass  weeds 
occur  in  fresh  or  brackish  water.  They  have  a  very  complex  organ- 
ization, representing  the  highest  development  of  the  green  algae, 
and  only  the  most  general  characters  will  be  given  Jjp^e.  The 
plants  vary  from  a  few  centimeters  (an  inch  or  so)  to  m&Fe  than  a 
meter  (several  feet)  long,  and  are  usually  much  branched.  The 
stems  are  slender  and  made  up  of  distinct  nodes  and  internodes. 
The  internodes  in  Nitella,  and  in  the  decorticated  species  of 
Cham,  consist  of  a  single  long  cylindrical  cell,  usually  several 

centimeters  long,  but  in 
Nitella  sometimes  30  cen- 
timeters (i  foot)  long.  At 
the  nodes  are  whorls  of 
Fig.  i9o.  short  cylindrical  out- 

Cyciosis  in  Nitella.  growths    resembling 

branches.  They  are  called  "  leaves  "  but  are  not  true  leaves. 
The  true  branches  arise  in  the  axils  of  these  "  leaf  "  whorls. 
The  internodes  in  most  species  of  Cham  are  covered  with  a 
cortex  of  cells.  The  sexual  organs  are  sperm  and  egg  cases 
(antheridia  and  oogonia).  The  stoneworts  are  remarkable  for 
the  striking  movement  of  the  protoplasm  in  the  cells.  The  proto- 
plasm flows  down  one  side  of  the  cell  and  back  on  the  other,  turn- 
ing at  the  ends. 


REVIEW   OF   THE  GREEN  ALGM  229 

REVIEW   OF  THE   GREEN   ALG^E. 

3700  Importance  of  studying  the  green  algae. — There  are 
several  important  reasons  for  studying  even  a  few  members  of  the 
green  algae.  First.  They  are  generally  of  simple  structure,  either 
single-celled  or  filamentous,  and  serve  as  excellent  objects,  easily 
prepared,  for  microscopic  study  of  the  cell  and  its  contents,  the 
processes  of  absorption,  plasmolysis,  etc.  Second.  The  sexual 
organs  and  methods  of  reproduction  are  simple  and  easily  studied. 
Third/  It  is  believed  that  some  members  of  the  green  algae,  exist- 
ing perhaps  ages  ago,  were  the  ancestors  of  the  higher  green  plants. 
It  is  therefore  of  interest  to  study  a  few  types  to  see  how  the  green 
algae  themselves  are  organized,  and  show  among  themselves  dif- 
ferent stages  in  this  process  of  evolution  from  simple  organisms 
consisting  of  a  single  cell  to  the  more  complex  ones  where  cells 
are  united  into  threads,  cell  plates  and  cell  masses. 

371.  Increase  in  the  complexity  of  the  plant  body. — The 
simplest  condition  of  the  plant  body  is  found  in  such  plants  as  the 
red  snow  plant  (H&matococcus).  The  plant  is  a  single  cell.  It 
multiplies  by  division  into  two  plants  which  are  associated  in  the 
parent  envelope  but  a  short  while,  when  they  escape  and  become 
independent.  In  such  a  plant  as  Pleurococcus  the  cells  are 
united  for  a  longer  period  during  multiplication,  while  in  the 
colony  algae  like  Pandorina,  and  the  water-net,  the  individuals 
are  permanently  united  in  a  loose  association.  Most  of  the 
desmids  are  single-celled  plants,  but  other  members  of  the 
conjugating  algae  are  filamentous.  They  are,  however,  really 
colony  algae,  since  each  cell  of  the  thread  is  identical  in  structure, 
and  potentially  identical  in  function;  each  cell  is  capable  of 
division  and  growth,  growth  not  yet  being  localized  at  any  definite 
growing  point,  or  area.  In  the  filamentous  algae  (Confervoideae), 
however,  while  the  cells  are  nearly  all  alike,  growth  is  localized, 
either  at  the  tips  of  the  threads  and  branches,  as  in  Cladophora 
and  Chcztophora,  or  in  definite  cells  at  any  point  in  the  thread, 
as  in  (Edogonium.  Many  of  the  filamentous  forms  are  branched. 
This  produces  a  more  complex  plant  body.  In  some  forms  the 


230  GENERAL   MORPHOLOGY   OF  PLANTS 

branching  is  so  close  and  compact  as  to  approach  tissue  masses 
in  the  cushion-like  mats  or  spheres  of  some  species  of  Coleoch&te 
and  Ch&tophora,  or  to  form  definite  leaf -like  cell  plates,  as  in  the 
sea  lettuce  and  the  shield  coleochcete. 

372.  Differentiation  of  sexual  organs. — In  the  lower  green 
algae,  the  one-celled  forms  (Protococcoideae)  and  the  conjugating 
algae  (Conjugatae),  the  gametes  are  usually  equal  in  size,  though 
in  some  forms  there  is  a  distinct  difference,  the  male,  or  sperm  cell, 
being  smaller  than  the  female,  or  egg  cell.  This  is  true  in  many 
of  the  filamentous  algae  (Confervoideae)  where  both  gametes  are 
motile  cells.  In  forms  like  (Edogonium,  and  Vaucheria  among 
the  siphon  algae  (Siphonales),  definite  and  distinct  organs  are 
developed  the  sex  of  which  can  be  recognized.  The  female  organ, 
the  egg  case  (oogonium),  is  large  and  contains  a  single  large  egg 
with  an  abundance  of  cytoplasm  to  furnish  nutriment  to  the  ger- 
minating egg.  The  male  organ,  the  sperm  case  (antheridium), 
is  smaller  in  size,  but  develops  usually  a  very  large  number  of 
small  sperm  cells.  These  escape  at  some  little  distance  from  the 
egg  case.  Of  the  large  number  of  sperms  formed  only  a  very  few 
ever  reach  the  egg  to  fertilize  it.  The  production  of  the  large 
number  of  sperms  is  a  provision  of  nature  to  make  sure  that  some 
by  chance  will  reach  the  egg.  Since  the  sperm  case  is  some  dis- 
tance from  the  egg  case  it  is  necessary  that  some  means  shall  be 
provided  to  bring  the  sperm  to  the  egg.  The  sperms  have  two, 
or  several,  cilia  and  are  free  swimming. 


CHAPTER   XXIV. 
ALG^  (Continued). 

THE   BLUE-GREEN   ALG^*   (CYANOPHYCE^). 

373.  General  characters. — The  blue-green  algae  include  some 
of  the  simplest  forms  of  plant  life.  In  some  respects  the  cell  is  less 
specialized  than  in  any  of  the  lowest  green  algce.  The  chloro- 
phyll is  not  in  definite  chlorophyll  bodies,  but  is  diffused  through- 
out the  protoplast  and  is  more  or  less  guised  or  obscured  by  a 
blue  pigment,  cyanin,  hence  the  name  blue-green  algae  or  Cyano- 
phycece  (bluish  algae).  A  few  of  them  have  brownish  or  red 
pigments.  The  red  shimmer  of  the  red  sea  is  caused  by  the 
presence  of  myriads  of  one  of  these  algae,  Trichodesmium  ery- 
thrceum,  which  has  a  red  pigment.  The  nucleus  is  not  so  dis- 
tinctly organized  as  in  most  plants.  According  to  some  the' deeply 
stained  nuclear  matter  (chromatin)  is  distributed  throughout 
the  cell  in  granules,  while  some  recent  investigations  seem  to  show 
that  there  is  a  definitely  organized  nucleus  but  less  specialized 
than  in  the  other  algae.  The  plants  exist  as  single  spherical  cells, 
spiral  cells,  as  colonies,  and  as  filaments  composed  of  numerous  •* 

*  To  THE  TEACHER.  In  first-year  courses  it  may  not  be  possible  to  study 
any  of  the  members  of  these  groups  with  the  aid  of  the  microscope.  Where 
possible,  however,  some  of  the  members  of  each  group  should  be  at  hand 
for  examination,  either  in  the  fresh  condition,  dried  and  mounted,  or  pre- 
served in  formalin  or  alcohol.  A  variety  of  species  mounted  on  cards  make 
interesting  objects  for  observation  of  color,  and  for  general  plant  form. 
The  rockweed  is  an  excellent  type  for  the  browns.  In  schools  located  in 
cities  near  the  seacoast  more  can  probably  be  done  in  the  study  of  the  browns 
and  reds  than  in  the  interior.  For  ,this  reason  several  types  of  these  are 
included.  In  more  advanced  classes  it  may  be  found  convenient  to  include 
some  microscopic  study  where  facilities  for  this  work  are  provided.  The 
Cambridge  Botanical  Supply  Company,  Cambridge,  Mass.,  makes  regular 
collections  and  shipments  for  schools  during  the  autumn. 

231 


232 


GENERAL   MORPHOLOGY   OF   PLANTS 


cells.  They  occur  in  fresh,  brackish,  or  salt  water,  and  on  damp 
rocks,  soil,  etc.  A  number  of  species  have  a  preference  for  foul 
water  or  waters  which  contain  organic  matter.  Some  of  these  on 
decaying  produce  very  foul  odors,  and  sometimes  occur  in  reser- 
voirs for  public  water  supply.  Here  they  may  become  a  great 
nuisance  and  a  menace  to  health.  They  can  be  destroyed  by 
adding  small  quantities  of  copper  sulphate  to  the  water  in  the 
reservoirs  without  injury  to  the  water  for  drinking  purposes.* 
Some  of  the  blue-green  algae  are  remarkable  for  growing  in  warm, 
or  hot,  water,  at  a  temperature  which  would  prevent  the  growth 
of  other  forms  of  plant  life  except  certain  bacteria.  In  the  hot 
water  flowing  from  the  geysers  at  Yellowstone  Park  some  of  these 
algae  live  in  water  at  a  temperature  of 
58°-68°  C.,  or  scantily  at  75°-77°  C. 
The  blue-green  algae  multiply  by  division 
of  the  cells  and  by  breaking  up  of  the 
colonies  or  threads.  In  the  filamentous 
forms  this  division  takes  place  much  as 
in  spirogyra,  by  simple  splitting  or  fission 
of  the  cells.  For  this  reason  they  are 
sometimes  called  fission  algae.  See  also" 
Bacteria,  Chapter  XXV.  Other  char- 
acters are  brought  out  in  a  study  of  the  examples. 

374.  Gloeocapsa. — This  is  a  one-celled  alga  which  forms  thin 
bluish-green  patches  on  the  ground  or  on  rocks,  logs,  etc.  Each 
cell  is  roundish,  and  is  surrounded  by  a  thick  capsule  of  a  gelati- 
nous nature  which  is  stratified  in  distinct  concentric  layers.  The 
cells  look  as  if  they  were  enclosed  in  gelatinous  capsules,  hence 
the  name  Glceocapsa.  In  multiplication  the  cells  divide  into  two 
daughter  cells  and  these  again  divide  in  like  manner.  The  divi- 
sions take  place  in  different  directions,  each  cell  having  a  distinct 
stratified  gelatinous  envelope,  and  several  of  these  enclosed  for  a 
time  in  the  envelope  of  the  parent  cell,  which  becomes  larger  with 
the  increase  in  the  number  of  the  cells. 

*  See  Bull.  No.  64  Bureau  of  Plant  Industry,  U.  S.  Dept.  Agr.,  1904,  and 
Bull.  No.  76,  1905. 


Fig.  191. 

Gloeocapsa. 


THE   BLUE-GREEN   ALG& 


233 


Fig.  192. 


A,  Oscillatoria  princeps:  a,  terminal  cell;  b,  c,  portions 
from  the  middle  of  a  filament.  In  c,  a  dead  cell  is  shown 
between  the  living  cells.  B,  Oscillatoria  froelichii:  b,  with 
granules  along  the  partition  walls. 


375.  Oscillatoria.—  Oscillatoria    is    one    of    the    filamentous 
forms,  and  some  of  the  species  are  very  common.     They  grow  in 
small  pools  or  in  large  bodies  of  rather  shallow  water.    They 
often  grow  on  the  soil  at 

the  bottom,  forming  dis- 
tinct films  or  sheets 
which  are  lifted  by  the 
bubbles  of  oxygen,  as  a 
result  of  photosynthesis, 
which  are  entangled  in 
the  meshes  of  the  film, 
and  then  float  as  a  scum 
on  the  surface  of  the 
water.  The  threads  are 
made  up  of  thin  disk- 
like  cells  which  are 
broader  than  long. 
Near  the  cross  walls  are  seen  distinct  but  small  granules  which  are 
supposed  to  be  reserve  food  products.  The  threads  of  Oscilla- 
toria exhibit  a  peculiar  motion;  they  sway  or  oscillate  back  and 
forth  slowly,  something  like  a  pendulum.  This  peculiar  motion 
of  the  threads  suggested  the  name  Oscillatoria.  They  also  glide 
slowly  in  the  direction  of  the  axis  of  the  thread.  The  division  of 
the  cells  is  a  transverse  fission.  The  threads  multiply  by  break- 
ing up  into  shorter  threads.  The  threads  are  surrounded  by  a 
thin  gelatinous  layer,  in  nature  similar  to  that  of  the  cell  wall. 
In  some  related  genera  the  threads  are  enclosed  in  a  thick  gelati- 
nous layer. 

376.  Nostoc. — The  Nostoc  plants  occur  on  damp  soil  or  wet 
rocks  in  thick  gelatinous  masses  or  nodules,  sometimes  quite  firm. 
The  cells  are  rounded  and  connected  like   a  string  of  beads. 
Numbers  of  these  bead-like  chains  are  scattered  through  the  jelly- 
like  mass.     Here  and  there  in  the  chain  are  larger  colorless  cells.* 
Division  of  the  cells  and  multiplication  of  the  threads  takes  place 
much  as  in  Oscillatoria.     A  related  plant  is  Anabcena,  which  is 

*  Called  heterocysts,  which  means  other  cells,  or  other  kind  of  cells. 


234  GENERAL  MORPHOLOGY  OF  PLANTS 

often  found  floating  on  the  water.     Some  of  the  cells  in  Anabczna 
become  much  longer  than  the  others  and  larger.     These  function 

as  spores  and  multiply  the  plant. 

377.  Review  of  the  blue-green 
algae.  —  In  addition  to  the  characters 
and  habits  given  under  general  char- 
acters it  is  to  be  noted  that  they  differ 
from  the  other  algae  by  the  absence 
of  sexual  reproduction,  or  at  least  that 
sexuality  has  not  yet  been  discovered 
in  the  group. 

THE    DIATOMS       (DIATOME^  : 

BACILLARIALES). 
A    &  df    C  378.    General    characters.^-The 

Fig.  i93-  ,.   A  ,          n    j        i 

Nostoc  linckii.    A,  filament  with     diatoms    are    single-celled   plants, 


fso!a[fde  few  remaining  loosely  joined  into 
filaments.  They  are  remarkable  for 
the  possession  of  a  silicious  skeleton, 

called  a  frustule,  which  encloses  the  protoplast.  This  skeleton  is 
in  two  parts  (valves)  resembling  a  box  with  its  cover,  some  of  the 
forms  resembling  an  old-fashioned  pill  box  (fig.  194).  Some  of  the 
frustules  are  remarkable  for  the  fine  and  beautiful  sculpturing,  and 
are  used  for  test  objects  in  determining  the  resolving  power  of 
high-grade  microscopic  lenses.  The  diatoms  occur  in  fresh  and 
salt  water.  They  exist  in  vast  numbers.  The  diatoms  together 
with  other  microscopic  plants  and  animals  form  what  is  called  the 
plankton  (wandering  life  of  the  sea)  of  fresh  and  salt  waters, 
especially  of  the  deep  waters.  Extensive  deposits  of  diatomaceous 
earth  several  feet  in  depth,  made  up  almost  entirely  of  the  skeletons 
of  diatoms,  exist,  for  example,  in  southern  England,  in  places  in 
the  Adirondack  Mountains,  at  Richmond,  Va.,  in  Nevada,  Cali- 
fornia, etc.  This  is  sometimes  used  as  a  polishing  powder.  The 
frustules  also  occur  in  guano. 

379.  The  frustules  of  the  diatoms  are  of  various  forms, 
elliptical,  oblong,  wedge-shaped,  circular,  etc.     Many  are  free, 


THE   BROWN   ALG& 


235 


Fig.  194- 

A  group  of  Diatoms:  c  and  d,  top  and  side 
lews  of  the  same  form;  e,  colony  of  stalked 


while  others  are  attached  to  objects  by  gelatinous  stalks,  the 

stalks  becoming  branched  as  the   diatoms  multiply  by  fission. 

They  possess  chlorophyll,  which,  however,  is  often  more  or  less 

obscured  by  brownish  or  yellowish  pigments.     In  multiplication 

the  protoplast  divides  in  line  with 

the  plane  between  the  two  valves, 

and  the  two  daughter  cells  sepa- 
rate each  with  one  valve.  The 

naked  part  of  the  protoplast  now 

deposits  a  new  valve  on  that  side. 

This  new  valve  must  necessarily 

fit  inside  of  the  old  one.     It  is 

evident,  therefore,  that  some  of 

the  new  plants  become   smaller 

and  smaller  with  each  successive 

division.  If  these  divisions  con- 
tinued, the  cells  would  in  time 

become  infinitely  small   But  they  Kerner-) 

finally  cast  off  both  valves  and  grow  to  the  normal  size.  Such  a 
cell  is  called  an  auxospore  (an  increasing 
spore).  A  process  of  conjugation  also  takes 
place  in  some  species  when  the  protoplasts 
from  two  cells  unite  to  form  an  auxospore. 


THE    BROWN  ALG^  (PH^OPHYCE^). 

380.  General  characters.  —  The  brown 
algae  chiefly  inhabit  salt  water  and  they  are 
widely  distributed  along  the  shores  of  oceans 
and  seas  from  arctic  to  tropic  regions.  While 
there  are  many  small  filamentous  forms, 
the  class  is  remarkable  for  the  number  of 
large  forms  exceeding  in  size  any  of  the  other 
algae.  In  many  of  these  the  plant  body  is 
itata,  forma  differentiated  into  stem  and  leaf-like  struc- 
tures,  and  the  stems  are  attached  to  rocks  by 


N°rth    Sea' 


236 


GENERAL   MORPHOLOGY   OF  PLANTS 


disks  or  root-like  holdfasts.  The  cells  contain  chromatophores 
with  chlorophyll,  and  in  addition  a  brown  pigment  (phycophczin  — 
algal  brown).  Asexual  reproduction  takes  place  in  some  forms 
by  zoospores  (Ectocarpus),  and  sexual  reproduction  by  the  union 
of  equal  motile  gametes.  In  other  forms  asexual  reproduction 
is  wanting,  but  multiplication  is  provided  for  by  the  immense 
number  of  eggs  produced  by  a  single  plant  (rockweed  =  Fucus), 
which  are  fertilized  by  much  smaller  sperms. 

381.  The  kelps. — The  kelps  include  the  largest  plants  found 
among  the  algae.  A  stalk,  either  short  or  long,  is  present,  which 
expands  into  one  or  many  leaf-like  expansions,  the  blades,  which 

are  often  very  stout  and 
large.  The  stalks  are 
attached  to  the  rocks  by 
haustoria,  or  grapplers, 
which  are  disk-like,  or 
in  many  species  resem- 
ble a  dense  tuft  of  short 
stout  roots.  The  giant 
kelp  (Macrocystis), 
which  grows  in  the 
Pacific,  is  200  to  300 
meters  (700-1000  feet) 
long.  The  genus  Lami- 
naria  is  widely  distri- 
buted and  occurs  on 
both  the  Atlantic  and 
Pacific  coasts.  Some 
of  these  have  simple 
strap-shaped  stout 
blades  10  meters  (30  feet)  or  more  long.  The  digitate  laminaria 
(L.  digitata)  has  a  broad  blade  which  is  split  lengthwise  into  a 
number  of  finger-like  processes.  The  sea  palm  (Poslelsia)  has  a 
stout  erect  cylindrical  stem  with  numerous  stout  blades  hanging 
from  the  top.  The  kelps  are  flexible  and  tough  and  are  able  to 
resist  the  pounding  of  the  surf  on  the  rocky  shore.  Asexual  repro- 


Fig.  196. 

Portion  of  plant  of  Fucus, 
showing  conceptades  in  en- 
larged ends;  and  below  the 
vesicles  (Fucus  vesiculosus). 


THE  BROWN   ALGA  237 

duction  takes  place  by  zoospores  formed  in  single-celled  spore 
cases  (sporangia)  in  large  groups  upon  the  blades.  Sexual 
reproduction  is  not  known. 

382.  The  rockweeds,  Fucus. — The  species  of  Fucus  are  very 
numerous  and  widely  distributed  in  the  temperate  and  arctic  seas. 
They  can  be  seen  often  in  vast  quantities  attached  to  the  rocks 
at  low  tide  when  they  are  often  uncovered.  The  short  stalk  is 
attached  to  the  rock  by  a  disk-like  holdfast.  The  blade  is  branched 
in  a  forked  manner,  and  the  middle  line  is  thickened  in  the  form 
of  a  midrib.  Growth  takes  place  in  a  small  depression  at  the 
apex  of  each  leaf.  Some  species  are  provided  with  large  bladder- 


Fig.  197.  Fig.  198. 

Section  of  conceptacle  of  Fucus,  showing  oogonia  Oogonium  of  Fucus  with 

and  tufts  of  antheridia.  ripe  eggs. 

like  vesicles  in  the  leaves  (Fucus  vesiculosus}.  The  sexual  organs 
are  developed  in  small  cavities  called  conceptades.  In  some 
species  the  male  and  female  organs  are  on  different  plants  (dice- 
cious),  in  others  they  are  in  different  conceptacles  of  the  same 
plant  (monoecious),  while  in  some  both  are  formed  in  the  same 
conceptacle  (hermaphrodite).  These  conceptacles  are  grouped  in 
definite  patches,  their  conical  mouths,  slightly  elevated,  giving 
a  punctate  appearance,  which  is  easily  observed.  The  concep- 
tacles are  oval  or  flask-shaped,  and  numerous  slender  filaments 
arise  from  the  bottom  and  sides  and  project  through  the  opening. 
The  egg  cases  are  large  rounded  bodies  attached  by  a  stalk  to  the 


238  GENERAL   MORPHOLOGY   OF  PLANTS 

wall  of  the  conceptacle,  each  of  which  contains  eight  eggs.  The 
eggs  are  set  free  by  the  rupture  of  the  wall,  and  escape  to  the 
outside.  The  sperm  cases  are  small  elliptical  bodies  borne  as 
branches  on  very  much  branched  filamentous  outgrowths  from 


Fig.  199.  Fig.  200. 

Antheridia   of   Fucus   on        Antheridia  of   Fucus  with         Eggs  of  Fucus  surrounded 
branched  threads.  escaping  sperms.  by  sperms. 

the  wall.  Each  sperm  case  develops  a  large  number  of  small 
biciliate  sperms,  which  also  escape  to  the  outside  in  the  sea  water. 
Here  they  swim  among  and  around  the  eggs,  often  causing  them  to 
revolve.  One  sperm  finally  enters  and  fuses  with  the  egg  nucleus. 
The  fertilized  eggs  which  reach  favorable  localities  start  to  grow 
within  a  day  and  develop  new  rockweed  plants. 

383.  Sargassum. — This  is  another  rockweed  which  is  inter- 
esting because  of  the  large  number  of  small  bladder-like  floats 
developed  as  lateral  outgrowths,  in  addition  to  the  thin  blades  and 
the  reproductive  branches.  Sargassum  is  sometimes  spoken  of 
as  gulf  weed.  Large  numbers  of  them  are  broken  away  by  the 
waves,  from  the  rocks  on  the  shores  of  the  West  Indies,  and 
are  carried  by  the  gulf  streams  to  the  open  sea  between  the  2oth 
and  4oth  parallels  of  latitude,  where  they  often  accumulate  in 
vast  numbers,  forming  what  are  called  ''Sargasso  seas,"  and  some- 
times interfere  with  navigation.  Here  they  grow  vegetative ly, 
but  are  not  known  to  fijuit  under  these  conditions. 


THE   RED    ALG& 


239 


384.  Uses  of  the  brown  algae. —  Some  of  the  kelps  (Lami- 
naria  japonica  and  L.  angustata)  are  used  as  food  by  the  Japa- 
nese and  Chinese.     Some  species  of  kelps  are  used  as  food  for 
cattle,  and  are  spread  upon  the  land  for  fertilizers  by  farmers  and 
peasants  along  the  north  Atlantic  coast  and  in  some  European 
countries.     L.  digitata  is  said  sometimes  to  be  employed  in  surgery. 
Iodine  is  extracted  from  some  kelps  and  rockweeds. 

THE   RED    ALG.E    (RHODOPHYCE^)- 

385.  General   characters. — The   larger   number  of   the   red 
algae  grow  in  the  sea,  but  a  few  grow  in  fresh  water.     They 
possess  chromatophores  with  chlo- 
rophyll, but  in  most  forms  this  is 

obscured  by  a  reddish  *  or  purplish 
pigment.  The  various  colors  are  red, 
purple,  brownish  red,  and  green. 
Some  forms  are  filamentous,  others 
are  more  bulky  and  cord-like  or 
strap-shaped,  while  others  are  leaf- 
like.  Nearly  all  forms  have  a 
greater  or  lesser  amount  of  a  gelat- 
inous or  slimy  substance  surround- 
ing the  parts  of  the  plant.  In  the 
method  of  reproduction,  and  in  the 
life  cycle  of  some  forms,  they  have 
reached  the  highest  stage  of  develop- 
ment of  any  of  the  algae.  Asexual 
reproduction,  where  it  occurs,  takes 
place  by  the  formation  of  groups 
of  spores,  four  in  each  group  (tetra- 
spores),  while  in  sexual  reproduc-  (After  Vmes-) 
tion  the  fertilized  egg  develops  a  large  number  of  spores. f  While 
these  methods  of  reproduction  are  characteristic  of  the  red  algae, 

*  Phycoerythrin. 

t  Called  carpospores,  i.e.,  fruit  spores,  because  the  mass  of  spores  is  the 
fruit. 


Fig.  202. 

A  red  alga  (Nemalion).      A,  sexual 
branches,  showing    antheridia  (a);    car- 


an     almost  "mature   cystocarp    (o)! 
the   disorganizing  trichogyne    (/)• 


240 


GENERAL   MORPHOLOGY   OF   PLANTS 


the  members  of  the  class  can  usually  be  recognized  by  their  reddish 
or  reddish  purple  color.  The  red  algae  are  usually  found  in  deeper 
water  than  the  brown  or  green  algae,  occupying  the  lower  zone  of 
the  alga-inhabited  region  below  ebb  tide,  where  the  waters  are 
more  dimly  lighted.  The  red  algae  are  more  sensitive  to  bright 
light  than  the  brown  and  green  and  suffer  discoloration  in  the 
brighter  light  region.  In  the  shade  they  grow  nearer  the  surface. 
Some  species  are  bright  red  when  growing  in  the  shade,  or  dull 
red  when  they  grow  in  brighter  light. 

386.  Nemalion. — The  plant  body  of  nemalion  is  a  slender, 
cylindrical,  branched  shoot.  The  central  strand  is  firm  and 
composed  of  delicate  threads.  It  is  covered  by  a  cortex  of  loose 
filaments  which  arise  as  lateral  branches'  and  extend  outward. 

It  represents  the 
simplest  type  of  sex- 
ual reproduction  in 
the  red  algae,  though 
there  are  filamentous 
forms  with  a  much 
more  simple  struc- 
ture of  the  thallus, 
i.e.,  the  plant  bcdy. 
The  sexual  organs. 
The  male  organs,  or 
sperm  cases  (anthe- 
ridia),'  are  small 
rounded  'cells  borne 
in  crowded  clusters,  on  short  branches,  at  the  end  of  a 
branch.  Each  sperm  case  contains  one  or  two  non-motile 
sperms.  The  female  organ.  This  is  borne  on  a  special  branch 
of  four  or  five  cells,  called  a  procarp.  The  terminal  cell  is  the 
egg,  but  is  called  a  carpogonium  in  the  red  algae,  because  it 
gives  rise  to  a  fruit  body,  the  cystocarp.  It  is  extended  into  a 
long  slender  process  called  the  trichogyne,  or  egg  hair.  The 
egg  with  its  hair  thus  resembles  very  closely  the  egg  case  of  Coleo- 
chaete.  Fertilization.  In  fertilization  a  sperm  comes  in  contact 


Fig.  203. 

Batrachospermum  ccerulescens.     Natural  size, 
during  the  summer  season  in  slow  running  water. 


It  grows 


THE  RED   ALGM 


241 


Fig.  204. 

Lemanea  fucina  which  grows  only  in  the  winter  in  turbulent  water 
of  streams.     Natural  size. 


Fig.  205. 
Polysiphonia  nigrescens  from  rock  at  Hellgate. 


242 


GENERAL   MORPHOLOGY   OF  PLANTS 


with  the  egg  hair.  Its  nucleus  makes  its  way  inside,  travels 
down  to  the  egg  and  fuses  with  its  nucleus.  The  fruit  case, 
cystocarp.  After  fertilization,  the  fertilized  egg  buds  out  in 
various  directions  and  produces  a  mass  of  closely  branched 
threads  with  short  cells.  The  terminal  cells  are  the  spores  (car- 
pos pores),  and  together  the  mass  is  called  the  cystocarp.  Each 
spore  is  capable  of  developing  a  new  nemalion  plant. 

387.  Batrachospermum    and    Lemanea    are    fresh-water 
forms  with  a  similar  method  of  sexual  reproduction.     The  former 
multiplies   also   by   non-motile   spores    (often   called  gonidia),   a 
single  spore  being  formed  in  a  small  globose  spore  case.     Batra- 
chospermum is  a  beautiful  plant,  green  or  purplish  in  color,  very 
profusely  branched   in   dense   tufts   around   a  central   axis.     It 
occurs  in  shallow  streams  and  pools.     Lemanea  is  remarkable 
for  the  fact  that  it  grows  only  during  the  winter  in  the  coldest 
part  of  the  year,  often  underneath  the  ice,  and  in  very  turbulent 
water. 

388.  Tetraspores  in  the  red  algae. — Many  of  the  red  algae 
have  an  asexual  method  of  reproduction  in  the  formation  of  tetra- 

spores.  Four  spores  are  borne 
in  a  single  spore  case  in  a  very 
regular  fashion.  In  many 
species,  and  perhaps  in  all, 
they  are  borne  on  special  plants 
which  do  not  bear  sexual  or- 
gans, as  in  Polysiphonia  vio- 
lacea,  Gracittariu,  Rhabdonia, 
etc. 

389.  Fertilization  in  the 
higher  red  algae. — The  proc- 
ess is  more  complicated  than 
in  Nemalion  and  the  lower 
forms.  The  sperm  cases  are 
developed  in  groups,  a  single  non-motile  sperm  being  formed 
in  each  sperm  case.  After  fertilization  the  fertilized  egg  does 
not  directly  form  the  spores.  It  conjugates  directly,  or  by  the 


Fig.  206. 

A  red  alga  (Callithamnion),  showing  spore- 
case  A,  and  the  tetraspores  discharged,  B. 
(After  Thuret.) 


THE   RED    ALGM 


243 


growth  of  long  filaments,  with  one  or  more  neighboring  cells 
on  other  branches.  This  is  probably  for  the  purpose  of  obtain- 
ing a  greater  amount  of  nutriment  for  the  development  of  the 
fruit  spores,  which  are  formed  oy  the  growth  and  branching  of 
this  neighboring  (auxiliary)  cell. 

390.  Uses  of  the  red  algae.— 
Many  of  the  red  algae  develop 
quantities  of  a  gelatinous  sub- 
stance in  their  tissues.  Several  of 
these  are  used  for  the  manufac- 
ture of  gelatines  and  agar-agar. 
Gracillaria  lichenoides  and  wrightii 
are  used  for  this  purpose,  the 
former  species  occurring  along 
the  coasts  of  China  and  India. 
Some  are  also  used  for  food.  The 
"  Irish  "  moss,  Chondrus  crispus, 
widely  distributed  in  the  northern 

Atlantic  ocean,  is  used  for  food  and  for  medicinal  purposes. 
Another  plant  used  for  similar  purposes  is  Gigartina  mamillosa, 
in  the  Atlantic  and  Arctic  oceans. 


Fig.  207. 
Irish  moss  (Chondrus  crispus). 


CHAPTER   XXV. 
BACTERIA. 

391.  General    characters. — The    bacteria   are   very   minute 
plants,  some  of  them  being  the  smallest  organisms  known.     An 
idea  of  the  size  of  very  small  ones  can  be  obtained  from  the  fact 
that  if  placed  side  by  side  it  would  take  5000  to  make  a  line  i  mm. 
long,  or  125,000  to  make  a  line  one  inch  long.     Like  the  fungi  they 
are  devoid  of  chlorophyll,  not  being  able  to   make  their  own 
carbohydrate  food.     A  few  can  fix  carbon  from  the  air  (see  para- 
graph 200).     They  are  dependent  on  green  plants  for  carbohy- 
drate food,  and  obtain  this  from  the  sugar  or  starch,  etc.,  in  other 
plants  upon  which  they  grow  as  saprophytes  or  parasites  (see 
Chapter  XV),  or  from  organic  matter  either  of  plant  or  animal 
origin  which  was  primarily  obtained  from  green  plants.     They 
are  in  the  form  of  rods,  or  spheres,  or  screws.     The  outer  layer  of 
the  wall  is  slightly  gelatinous,  and  this  peculiarity  is  made  use  of 
in  fixing  them  to  glass  slips  in  mounting  them  for  study,  by  the 
use  of  heat.     Some  of  the  bacteria  are  non-motile,  while  others 
are    motile.     The    motion   is   usually    a   jerky   irregular   rotary 
motion,  but  the  spiral  forms  dart  rapidly  along  like  a  forward- 
moving  screw.     The  motile  ones  are  provided  with  delicate  cilia 
(fig.  101),  which  cannot  be  made  visible  except  by  special  treat- 
ment with  mordants  and  stains.     They  multiply  by  simple  fission 
as  in  the  blue-green  algae.     Resting  spores  are  formed  in  many 
species  by  the  condensation  of  the  protoplasm  into  a  small  shining 
body  within  the  cell  which  is  able  to  resist  greater  extremes  of 
heat,  cold,  dryness,  etc. 

392.  The  principal  forms  of  bacteria  and  their  methods 
of  multiplication. — Many  of  the  rod-like  bacteria  belong  to  the 
genus  Bacillus.     In  multiplication  this  rod  divides  into  two  short 
rods  which  increase  in  length  to  the  size  of  the  parent  rod.     In 

244 


BACTERIA 


245 


some  species  these  daughter  rods  separate  very  readily,  while  in 
others  they  hold  together  for  some  time,  making  a  long  and  fine 
thread  which  later  separates  into  the  separate  rods.  Beggiatoa 
forms  long  filaments  of  short  cells  similar  to  those  of  Oscillatoria 
but  lacking  the  blue-green  color.  The  screw  or  spiral  forms  are 
found  in  the  genera  Spirillium,  Vibrio,  etc.  They  also  multiply 
by  cross  division  of  the  cells.  The  round,  or  spherical,  forms  are 
found  in  a  number  of  different  genera  according  to  the  method  of 
association  of  the  individuals.  In  Micrococcus  (minute  berry)  the 
rounded  cells  divide  into  two  which  quickly  separate.  In  Strepto- 
coccus with  rounded  cells,  the  cells  after  dividing  remain  in  chains 
similar  to  the  bead-like  chains  of  Nostoc.  In  Sarcina  the  rounded 
cells  divide  in  two  or  three  directions,  the  cells  remaining  held 
together  in  small  cubical  groups  for  a  time. 

393.  The  work  of  bacteria  in  decay,  fermentation,  and 
disease. — For  a  discussion  of  this  see  paragraphs  220-223,  which 
should  be  studied  in  connection  with  this  chapter. 

394.  Comparative  review  of  the  bacteria. — The  bacteria 
resemble  the  fungi  in   that  chlorophyll  is   absent.     Because  of 
their  method  of  multiplication  by  simple  division,  or  cutting  in  two 
of  the  cells,  which  is  sometimes  called  fission,  they  are  called 

.fission  fungi  or  Schizomycetes,  and  by  some  are  classed  with  the 
fungi.  But  this  method  of  fission  is  like  that  of  the  blue-green 
algae,  which  they  also  resemble  in  the  variety  of  forms  and  asso- 
ciation of  cells,  as  well  as  in  the  simple  condition  of  the  proto- 
plast, and  the  slimy  covering  of  the  cell  walls.  For  these  reasons 
some  consider  them  more  closely  related  to  the  blue-green 
algae,  and  place  them  in  a  class  called  Schizophycecz,  with  two 
sub-classes,  the  Cyanophyceae  (blue-green  algae)  and  the  Schizo- 
mycetes (Bacteria).  Still  others  place  them  in  a  class  (Schizomy- 
cetes) distinct  from  either  the  fungi  or  blue-green  algae.  This 
seems  to  be  the  better  arrangement. 


CHAPTER   XXVI. 
FUNGI. 

GENERAL    CHARACTERS;    MOLDS;    MILDEWS. 

395.  General  characters. — The  fungi  are  plants  of  a  low 
grade  of  organization,  in  this  respect  resembling  the  algae.  In 
fact  they  stand  as  a  parallel  group.  The  plant  body,  or  thallus, 
of  the  lower  and  higher  forms  in  structure  is  very  much  like  that 
of  many  of  the  algae,  and  some  of  the  methods  of  reproduction  are 
very  similar  to  methods  of  reproduction  in  some  of  the  algae. 
There  are,  however,  some  features  of  structure  and  methods  of 
nutrition  in  which  they  differ  strikingly  from  the  algae.  First.  The 
fungi  are  entirely  devoid  of  chlorophyll  as  well  as  the  bodies 
(plastids)  which  are  the  basis  of  the  chlorophyll  bodies.  Second. 
Not  having  chlorophyll,  photosynthesis  does  not  take  place,  and 
they  cannot  make  their  own  carbohydrate  food,  i.e.,  the  sugar  and 
starch.  They  are  dependent  on  chlorophyll-bearing  plants  for 
this  food,  just  as  animals  are.  Third.  They  live  chiefly  on  organic 
matter,  either  dead  or  living  plants  or  animals,  or  their  remains. 
The  fungi  according  to  their  method  of  nutrition  can  be  grouped 
in  two  categories:  first,  Saprophytes,  which  live  on  dead  or 
decaying  organic  matter  (plants  and  animals);  second,  Parasites, 
which  live  upon,  or  in,  living  plants  and  animals  (see  Chapter 
XV).  In  defining  the  structural  elements  of  the  fungi  it  is  con- 
venient to  speak  of  two  parts:  first,  the  vegetative  or  growing 
part,  and  second,  the  fruiting  or  reproductive  part. 

To  THE  TEACHER.  At  least  three  types  of  the  fungi  should  be  studied, 
one  of  the  molds  (Mucor  or  Rhizopus),  a  powdery  mildew  (Microsphaera), 
and  a  mushroom.  Other  examples  in  each  class  of  the  Fungi  can  be  used 
as  illustration,  or  where  more  time  can  be  given  to  the  practical  work  the 
teacher  can  select  suitable  examples  from  those  described  in  the  text.  One 
lichen  should  also  be  studied. 

246 


FUNGI,   GENERAL   CHARACTERS  247 

396.  The  vegetative  or  growing  part  of  the  fungi. — In 

nearly  all  the  fungi,  the  growing  or  vegetative  part  consists  of 
delicate  filamentous  or  thread-like  growths.  These  threads  are 
called  mycelium,  or  a  single  thread  of  the  mycelium  is  often  called 
a  hypha,  which  may  be  simple  or  somewhat  branched.  A  mat 
or  tangle  of  hyphae  is  spoken  of  as  mycelium.  In  some  fungi 
the  mycelium  is  scantily  developed,  while  in  others  dense  mats 
or  stout  cords  are  formed. 

397.  The  fruiting  stage  or  part. — In  most  of  the  fungi  special 
hyphae,  called  sporophores  (spore  bearers),  are  developed  from  the 
vegetative  mycelium.     These  are  simple  or  branched,  single  or  in 
fascicles,  as  in  the  molds  and  mildews;  or  united  into  large  and 
compact  bodies,  as  in  the  mushrooms.     Asexual  reproduction  takes 
place,  in  most  fungi,  by  the  formation  of  asexual  spores,*  either 
motile  or  non-motile.     In  many  species  there  are  several  different 
kinds  of  asexual  spores  on  separate  forms  or  parts  of  the  fungus 
(polymorphism);  sometimes  these  different  forms  occur  on  dif- 
ferent hostt  plants  (heteracism),  as  in  the  wheat  rust.     Sexual 
reproduction  is  by  conjugation  in  some  of  the  lower  forms,  or  by 
fertilization  of  an  egg  by  a  sperm.     The  details  must  be  sought  in 
a  study  of  different  types. 

398.  The  three  classes  of  fungi. — While  little  attention  can  be 
given  here  to  the  classification  of  the  fungi,  it  may  be  well  to 
outline  briefly  the  three  great  classes.     In  the  lower  fungi  the 
mycelium  is  siphon-like,  i.e.,  similar  to  the  threads  of  the  siphon 
algae.     The  characteristic  fruit  structure  is  a  spore  case  (sporan- 
gium) with  usually  a  variable  and  indefinite  number  of  spores. 
These  fungi  form  what  is  called  the  sporangium  series  and  make 
up  the   Class  Phycomycetes  (alga-like  fungi).     Here  belong  the 
molds,  water  molds,  downy  mildews,  etc. 

399.  In  the  higher  fungi  the  mycelium  is  septate,  i.e.,  there  are  nu- 
merous cross  walls  in  the  mycelial  threads.     There  are  two  classes. 

400.  First.  The  characteristic  fruit  structure  is  a  sac-like  body 
called  an  ascus,  which  contains  usually  a  regular  and  definite 

*  Conidia,  or  gonidia,  or  chlamydospores. 

t  The  host  is  the  plant  on  which  a  fungus  is  parasitic. 


248  GENERAL   MORPHOLOGY   OF   PLANTS 

number  of  spores.  In  the  great  majority  there  are  eight  spores 
in  an  ascus,  while  in  some  there  are  16,  32,  64,  128,  or  even  6,  4, 
2,  and  in  a  few  i,  or  a  variable  number.  These  asci  are  usually 
grouped  together  in  extended  surfaces  or  in  conceptacles.  These 
make  up  the  Class  Ascomycetes.  Here  belong  the  cup  fungi, 
morels,  black  fungi,  etc. 

401.  Second.  In  the  other  class  the  characteristic  fruit  structure 
is  a  short  and  specialized  cell  or  hypha,  which  is  single-celled,  or 
four-celled  in  the  lower  forms,  and  which  bears  on  the  outside 
a  definite  and  regular   number   of    spores,  usually  four.     This 
specialized  cell  or  hypha  is  called  a  basidium,  which  is  the  Latin 
word  for  club,  since  this  specialized  cell  is  usually  club-shaped. 
These  make  up  the  Class  Basidiomycetes.     Here  belong  the  smuts, 
rusts,  mushrooms,  toadstools,  bracket  fungi,  puff  balls,  etc.     In 
studying  examples  of  the  fungi  it  will  be  convenient  to  select  them 
from  these  three  classes. 

ALGA-LIKE,   OR  SPORANGIUM-FRUIT  FUNGI. 

(Class  Phycomycetes.) 

The  Conjugating  Molds. 

402.  The   bread    mold.* — This   fungus  is  very  widely  dis- 
tributed  over    the    world    and    grows    on    a    great   variety   of 
dead    vegetable    substances,    and    is,    therefore,    a    saprophytic 
fungus.     It  sometimes  approaches  the  life  habits  of  a  parasite, 
for  it  is  often  found  causing  a  serious  rot  of  stored  vegetables, 
especially   sweet   potatoes,  beets,  etc.,  when    the    storehouse  or 
cellar  is  not  well  ventilated  and  the  temperature  is  too  high. 
It  is  called  the  bread  mold,  or  black  mold  (Rhizopus  nigricans], 
because  it  often  occurs  on  stale  bread  in  close  or  damp  places,  in 
age  becoming  black  because  of  the  dark  spore  masses  and  hyphae. 

*  To  THE  TEACHER.  If  there  is  time  for  the  practical  study  of  only  one 
of  the  fungi  of  this  class  there  is  no  better  example  than  the  bread  mold. 
The  molds  can  be  further  illustrated  by  some  examples  of  the  white  rust,  the 
downy  mildews,  etc.,  preserved  on  sheets,  and  of  the  water  mold  in  culture. 
Where  more  time  is  available  for  practical  study  these  will  serve  as  examples. 


FUNGI,    BLACK  MOLD 


249 


The  spores  are  very  numerous  and  float  readily  in  the  air,  so  that 
if  a  piece  of  bread  or  cooked  potato  is  left  exposed  in  a  room  or 
out  of  doors  for  a  day  or  less,  and  then  covered  in  a  pan  with 
some  moist  paper,  in  a  few  days  the  mold  will  appear.  The 
mycelium  is  white  and  forms  an  abundant  growth  of  threads 
forming  the  white  glistening  mat  which  spreads  over  the  bread  or 
other  substances. 

403.  Asexual  reproduction. — The  mycelium  is  the  vegetative 
or  growing  stage  of  the  fungus.  Within  a  day  or  so  after  the 
mycelium  begins  to  form,  asex- 
ual reproduction  begins  and 
at  the  same  time  the  mycelium 
continues  to  spread.  Here  and 
there  upon  a  thread  of  my- 
celium, erect  hyphae  arise  in 
tufts  of  three  to  five  or  more 
(fig.  208).  The  ends  of  these 


branches  become  enlarged  into 
a  rounded  body,  the  spore  case 
or  sporangium,  and  the  proto- 
plasm is  separated  from  that  of   the  stalk,  or  sporophore  (some- 
times called  sporangiophore),  by  an  arched  wall,  the  columella. 


Fig.  208. 

Group  of  sporangia  of  a  mucor  (Rhizopus 
nigricans),  showing  rhizoids  and  the  stolon 
extending  from  an  older  group. 


Fig.  209. 

A  mucor  (Rhizopus  nigricans);  at  left,  nearly  mature  sporangium  with  columella,  showing 
within;  in  the  middle  is  ruptured  sporangium  with  some  of  the  gonidia  clinging  to  the  colu- 
mella; at  right,  two  ruptured  sporangia  with  everted  columella. 

At    maturity    the    sporangium    wall    disintegrates    so    that    the 
spores  are  easily  set  free.     The   columella   is  often  very  large 


25° 


GENERAL   MORPHOLOGY   OF  PLANTS 


and  might  be  mistaken  for  the  sporangium  after  the  spores  are 
scattered.  It  sometimes  collapses  as  shown  in  fig.  209.  At  the 
base  of  the  clusters  of  sporophores  is  a  tuft  of  delicate,  branched, 
rootlet-like  threads  called  rhizoids.  These  as  well  as  the  sporo- 
phores become  blackish  in  color.  The  larger  number  of  these 
clusters  of  sporophores  are  borne  at  intervals  on  distinct  creeping 
hyphae,  which  rise  into  the  air  and  then  touch  the  substratum 
here  and  there  like  the  stolon  of  the  strawberry  vine,  or  the  leaf 
of  the  walking  fern,  developing  a  cluster  of  sporophores  at  each 
point  of  contact.  These  stolon-like  hyphae  will  spread  off  from 
the  bread  onto  the  sides  of  the  vessel.  Because  of  this  peculiar 
stolon-like  hypha  this  mold  is  sometimes  called  the  stolon  bearer 
(Mucor  stolonifer,  another  technical  name  sometimes  applied). 
The  name  Rhizopus  is  given  to  the  plant  because  of  the  rhizoids  at 
the  foot  of  the  sporophores. 

404.   Germination  of   the   spores  and   character   of   the 
mycelium. — The  spores  germinate  when  the  temperature  and 


Fig.  210. 
Spores  of  Mucor,  and  different  stages  of  germination. 

moisture  conditions  are  suitable.  They  absorb  water  and  swell 
to  a  large  size,  then  a  protuberance  appears  on  one  side,  which  is 
the  beginning  of  a  hypha  or  mycelial  thread.  This  is  called  the 
germ  tube,  because  it  resembles  a  short  tube  from  the  germinating 
spore.  This  elongates  quite  rapidly,  and  branches  profusely, 
sending  branches  radially  in  all  directions  in  the  food  substance, 
and  others  into  the  air  if  the  air  is  moist.  The  mycelium  is  con- 
tinuous, i.e.,  it  is  not  divided  up  into  cells  by  cross  walls,  The 


FUNGI,    BLACK   MOLD 


251 


protoplasm  is  coarsely  granular  and  shows  numerous  vacuoles  of 
varying  size  (fig.  210).  The  protoplasm  shows  streaming  move- 
ments. It  flows  along  in  a  thread-like  stream,  or  in  other  cases 
there  may  be  smaller  currents  up  and  down  the  thread.  There 
are  large  numbers  of  nuclei  in  the  protoplasm,  but  they  cannot 
be  demonstrated  without  careful  treatment  according  to  certain 
technical  methods.  Cross  walls  appear  where  reproductive 
bodies  or  organs  are  formed,  and  rarely  here  and  there  in  old 
mycelia 

405.   Sexual  reproduction. — Sexual  reproduction  takes  place 
by  conjugation.     This  occurs  between  two  threads  or  branches  of 


Fig.  211. 
Rhizopus  nigricans.     Different  stages  in  conjugation  of  +  and  —  strains  to  form  zygospores. 

mycelium  which  are  of  an  opposite  sex  nature.  One  cannot  dis- 
tinguish between  male  and  female  according  to  the  size  and  appear- 
ance of  the  conjugating  branch,  though  sometimes  at  a  later  stage 
one  becomes  much  larger  than  the  other.  The  branches  meet 
at  their  ends,  and  each  swells  into  a  club-shaped  body.  A  cross 
wall  now  cuts  off  a  body  of  protoplasm  in  the  end  of  each  branch. 


252 


GENERAL   MORPHOLOGY    OF   PLANTS 


This  cell  is  the  gamete  case  (gametangium)  and  the  protoplasm 
in  each  is  a  gamete  (fig.  211).  The  remaining  part  of  each 
branch  is  a  suspensor,  so  called  because  it  suspends  the  gamete 
cases.  The  walls  between  the  gametes  dissolve  so  that  there  is  a 
mixing  or  fusion  of  the  protoplasm  of  the  two  gametes.  This 
united  body  enlarges,  and  the  wall  becomes  thick,  black, 
and  rough  with  small  wart-like  protuberances.  This  is  the 
zygospore. 

406.   Germination  of  the  zygospore.  —  The  zygospore  of  the 
bread  mold    has  not  yet  been  found  to  germinate,  but  that  of 

a  related  mold  (Mucor  mucedo 
Linn.)  has.  When  it  germinates 
it  produces  at  once  a  sporophore 
and  spore  case  containing  numer- 
ous asexual  spores.  These  are 
scattered  and  produce  the  my- 
celium and  successive  cycles  of 
the  asexual  stage. 

407.  The  bread  mold  is 
dioecious.*  —  In  the  bread  mold 
(R.  nigricans)  the  conjugating 
branches  always  arise  from  dif- 
ferent plants.  The  two  branches 
of  an  opposite  sex  nature,  or 
strain,  never  arise  from  the  same 
plant,  that  is  from  the  mycelium 
which  came  from  a  single  spore. 
There  must  be  two  different  colo- 
nies of  mycelia,  each  from  a  single 
spore  of  opposite  sex  natures,  one 
corresponding  to  the  male  and 

° 
one    to    the    female.        These    tWO 

must   be  prowing   Side   by  side   Or 

mixed  so   that   branches   which 
would  be  of  opposite  sex  natures  can  meet  and  conjugate.    Under 
*  Heterothullic,  because  there  are  two  sorts  of  thalli,  male  and  female. 


Fig>  2I2i 
Formation  of  zygospores  im  a  moid  (Mucor 

mucedo  >.  A,  two  hypha;  in  contact,  end  to 
end;  B,  the  terminal'gametes;  C,  later  stage, 
the  gametes  fusing;  D,  a  ripe  zygospore;  £, 
germination  of  a  zygospore,  the  filament 
forming  a  sporangium  at  once  in  this  case. 

(After  Brefeid.) 


FUNGI,   SEX   IN   MUCORS  253 

natural  conditions  these  two  strains  or  sets  of  mycelia  of  opposite 
nature  are  sometimes  growing  mixed  together,  but  more  often, 
probably,  the  two  strains  are  growing  separately.  If  one  obtains 
a  culture  of  only  one  strain  on  the  bread  no  zygospores  will  be 
produced.  But  if  the  mixed  strains  are  obtained,  then  zygospores 
will  be  produced  in  number  down  in  the  lower  part  of  the  vessel 
where  it  is  moist,  usually  in  small  spaces  between  the  paper  and 
the  wall  of  the  vessel  or  bread.  It  will  be  remembered  that  the 
plant  body  of  an  alga  or  a  fungus  is  called  a  thallus.  The  mycelium 
from  a  single  spore,  then,  is  a  thallus.  Since  two  different  thalli 
of  the  bread  mold  are  necessary  to  bring  about  conjugation  and 
produce  zygospores,  such  a  thallus  plant  is  said  to  be  heterothallic, 
because  other  or  different  thalli  must  be  brought  together  for 
sexual  reproduction.  They  are  also  said  to  be  dioecious.  The 
Mucor  mucedo  above  mentioned  is  also  dioecious.  In  some  of  the 
molds  there  is  a  difference  in  the  size  of  the  two  different  thalli; 
the  one  supposed  to  represent  the  female  is  larger  and  is  by  some 
indicated  as  + .  The  other  being  smaller  is  indicated  by  — .  By 
extension  +  and  —  are  applied  to  corresponding  strains  in  species 
where  the  thalli  are  of  equal  size. 

408.  Monoecious  Mucors.* — Some  of  the  mucors  are  monoe- 
cious,!   i-C-j   both   sexes   are   present    in   the    mycelium    from   a 
single  spore.     This   is  true  in  the  mushroom   mold  (Sporodinia 
grandis),  a  common  mold  growing  on  decaying  mushrooms  in 
the  woods. 

409.  Nature  of  the  spores  in  the  germ  sporangium. — The 
name  germ  sporangium  is  by  some  applied  to  the  spore  case  which 
is   formed   from   the   germinating   zygospore.     Since    the    sexes 
become  mixed  in  the  zygospore  of  the  dioecious  species  they  must 
be  separated  again,  otherwise  the  species  would  become  monoecious. 
This  separation  takes  place  in  Phycomyces  nitens  in  the  formation 
of  the  spores  in  the  -germ  sporangia,  so  that  there  are   +  and  — 
spores  mixed  in  a  single  spore  case.     In  Mucor  mucedo  they  are 

*  Mucorinese,  or  Mucorales.    The  order  containing  different  genera  and 
many  species  of  Mucors  is  called  Mucorinece,  or  Mucorales. 
t  Homothallic,  because  all  the  thalli  are  alike  sexually. 


254 


GENERAL   MORPHOLOGY   OF   PLANTS 


separated  before  the  formation  of  the  germ  sporangium,  so  that 
the  spores  in  one  germ  sporangium  from  a  single  zygospore  are 
all  +  while  in  another  they  are  all  — . 

The  Water  Molds. 

410.  The  water  mold. — These  fungi  grow  on  dead  insects  or 
other  animals  in  the  water,  or  even  on  dead  plant  parts.  They  are 
very  common  on  dead  insects,  and  sometimes  are  seen  growing  on 


Fig.  213. 

Sporangia    of   Saprolegnia,   one  with  zoospores  escaping   and  passing   through  the  first 
swarming  period.      Below,  passing  through  second  swarming  period  and  then  germinating. 

living  but  weakened  fish  and  other  aquatic  animals.  They  are 
easily  obtained  by  collecting  algae  with  some  of  the  ditch  or  pond 
water  in  which  they  grow,  and  throwing  dead  flies  into  it.  The 
mycelium  grows  through  the  body  of  the  fly,  and  then  long  white 
threads  radiate  out  in  the  water  all  around  the  insect.  The  myce- 
lium is  coarsely  granular,  vacuolate,  and  continuous. 


FUNGI,    WATER   MOLDS  255 

411.  Asexual  reproduction. — This  takes  place  by  the  forma- 
tion of  spore  cases.     In  the  common  water  mold  (Saprolegnia}, 
the  spore  cases  are  long  and  cylindrical.     They  are  formed  in  the 
ends  of  threads  or  branches  by  a  cross  wall  which  cuts  off  the  pro- 
toplasm from  the  rest  of  the  thread.     The  spore  case  is  usually 
stouter  than  the  thread  which  bears  it.     The  spores  are  oval,  with 
two  cilia  on  the  smaller  end.     The  spores  swim  out  of  an  opening 
at  the  end  and  after  passing  through  a  first  swarming  period 
round  up  and  pass  a  resting  period.     Then  they  slip  out  of  the 
thin  membrane  surrounding  the  protoplasm,  and  are  bean-shaped, 
with  two  cilia  on  the  concave  side.     They  now  pass  through 
another  swarming  period.     Then  they  come  to  rest  and  germinate, 
if  they  have  found  a  suitable  substratum. 

412.  Sexual  reproduction. — Sexual  organs,  sperm  and  egg 
cases  (antheridia  and  oogonia),  are  formed  on  the  mycelium  of  the 


Fig.  214. 

Fertilization  in  Saprolegnia,  tube  of  antheridium  carrying  in  the  nucleus  of  the  sperm 
cell  to  the  egg.  In  the  right-hand  figure  a  smaller  sperm  nucleus  is  about  to  fuse  with  the 
nucleus  of  the  egg.  (After  Humphrey  and  Trow.) 

water  molds,  but  it  is  a  disputed  question  if  fertilization  takes 
place.  The  egg  case  in  some  species  is  round,  in  others  elongate. 
It  is  formed  on  a  short  branch  or  directly  in  a  thread,  and  is  sepa- 
rated by  a  cross  wall.  In  Saprolegnia  several  eggs  are  formed  in  a 
single  egg  case.  The  sperm  case  is  a  slender  branch  which  coils 
partly  around  the  egg  case  and  sends  a  fertilization  tube  inside  and 
in  contact  with  the  eggs.  Some  claim  that  a  sperm  nucleus  from 
the  sperm  case  unites  with  the  egg  nucleus  to  bring  about  fertili- 
zation, while  others  deny  it.  It  is  certain  that  in  some  species 
sperm  cases  are  not  formed,  and  yet  the  eggs  ripen  without  fertili- 


256 


GENERAL   MORPHOLOGY   OF  PLANTS 


zation  and  germinate.*  This  ripening  and  functioning  of  eggs 
without  fertilization  is  known  to  occur  in  some  animals,  notably 
the  plant  lice,  and  in  some  of  the  flowering  plants. 

413.  Stoppage  of  drain  pipes  by  water  molds. — Some  of  the 
water  molds  (notably  Leptomitus  lacteus)  grow  in  waste  pipes  and 
drains  from  refrigerators,  cider  presses,  etc.,  and  cause  annoy- 
ance by  stopping  the  flow  of  the  waste  water.  Flushing  with 

water  often  clears  the  drain, 
but  if  the  fungus  continues  to 
be  troublesome  its  growth  can 
be  prevented  by  flushing  the 
drain  now  and  then  with  a 
weak  solution  of  blue  vitriol. 

i 

The  Downy  Mildews  and 
White  Rust. 

414.  The  downy  mil- 
dews.— The  downy  mildews 
received  this  name  from  the 
numerous  sporophores,  often 
branched,  which  are  crowded 
in  spots  on  the  parts  of 
plants  which  they  attack. 
These  crowded  sporophores 
look  like  so  much  down, 
and  the  affected  areas  have 

Fig  2is  also  a  mildewed  appearance. 

Downy  mildew  of  grape  (Pksmopora  viticoia),  They  are  true  parasites,  since 

showing  tuft  of  gonidiophores  bearing  gonidia,  also  ,  i  IT-  i       ±  j 

intercellular  mycelium.     (After  Millardet.)  they  attack  living  plants  and 

often  cause   serious  diseases 

of  cultivated  plants,  entailing  thousands  of  dollars  of  loss  to  the 
horticulturist  or  farmer.  Some  of  the  important  diseases  caused 
by  them  are  downy  mildew  of  the  grape  and  cucumber,  onion 


*  This  germination  of  eggs  which  have  not  been  fertilized  is  sometimes 
called  parthenogenesis. 


FUNGI,   DOWNY   MILDEWS 


257 


blight,  early  potato  blight,*  etc.  During  1849  the  potato  blight 
caused  almost  the  complete  loss  of  the  potato  crop  in  Ireland,  and 
a  serious  famine  resulted. 

415.  The    mycelium.— The    mycelium    attacks    the    leaves, 
stems,  and  fruit.     The  germ  tube  from  a  spore  enters  at  a  stomate 
of  the  leaf  or  between 

epidermal  cells.  The 
mycelium  grows  be- 
tween the  cells  in  the 
intercellular  spaces, 
and  is  thus  said  to 
be  intercellular.  The 
mycelium  is  con- 
tinuous and  multinu- 
cleate.  It  develops 
short  special  branch- 
es, of  different  form 
in  different  species, 
which  penetrate  the 
cells  and  take  food 
from  the  protoplasm 
(fig.  216).  This  kills 
the  cells,  and  dead 

spots  appear  on  the  leaves,  fruit,  and  stems,  or  the  death  of  leaves, 
fruit,  and  stems  is  the  result  in  some  cases. 

416.  Asexual     reproduction.  —  In     asexual     reproduction 
branches    arise    from   the    intercellular    mycelium,    which    issue 
through  the   stomates,  often  several  together.     Outside  of  the 
leaf  these  usually  branch  (in  a  different  manner  in  different  genera). 
These   are  the  sporophores  or  conidiophores.     The  tips  of  the 
branches  bear  oval  spores  (conidia).     When  these  fall  away  they 
germinate,  the  manner  of  germination  depending  on  the  genus  of 

*  The  remedy  for  these  blights  is  to  spray  the  plants  with  Bordeaux  mix- 
ture before  they  become  infested.  Spray  when  the  leaves  are  young,  and 
then  at  intervals  of  two  to  three  weeks.  In  the  case  of  the  grape  vine  the 
first  spray  should  be  applied  .before  the  buds  burst. 


Fig.  216. 

Intercellular  mycelium  with  haustoria  entering  the  cells! 
A,  of  Cystopus  candidus  (white  rust);  B,  of  Peronospora 
calotheca.  (De  Bary.) 


258  GENERAL   MORPHOLOGY   OF   PLANTS 

the  fungus.  In  the  onion  mildew  (Peronospora  schleideniana)  the 
spore  germinates  by  a  germ  tube  which  forms  the  mycelium. 
In  the  grape  downy  mildew  (Plasmopara  mticola)  the  protoplasm 
of  the  spore  (conidium)  first  divides  into  several  smaller  bodies 
which  form  bean-shaped  zoospores  with  two  lateral  cilia.  These 
escape  from  the  conidium  (really  a  spore  case  in  the  downy  mil- 
dews), swim  about  for  a  time,  then  come  to  rest,  germinate  and 
produce  mycelium  again  if  they  are  favorably  situated.  The 
spores  of  the  potato  blight  germinate  in  both  ways.  Successive 
crops  of  the  asexual  stage  are  rapidly  formed,  and  the  disease 
spreads. 

417.  Sexual  reproduction. — This  takes  place  by  the  forma- 
tion of  the  sexual  organs,  sperm  and  egg  cases  (antheridia  and 
oogonia),  and  the  fertilization  of  the  egg.  The  egg  case  is  a 


Fig.  217. 

Fertilization  in  Peronospora  alsinearum;  tube  from  anther idium  carrying  in  the  sperm 
nucleus  in  figure  at  the  left,  female  nucleus  near;  fusion  of  the  two  nuclei  shown  in  the  two 
other  figures.  (After  Berlese.) 

short  branch  which  swells  out  into  a  large  rounded  body.  A 
single  egg  is  formed  from  the  centrally  located  protoplasm,  leav- 
ing a  layer  of  protoplasm  (periplasm)  around  the  outside  which 
does  not  take  part  in  the  formation  of  the  egg.  The  sperm  case  is 
a  slender  branch  which  rests  against  the  wall  of  the  egg  case  and 
develops  a  slender  fertilization  tube,  which  penetrates  to  the  egg. 
This  carries  in  the  sperm  nucleus,  which  fuses  with  the  egg  nucleus 
to  bring  about  fertilization  (fig.  217). 

418.  The  white  rust. — An  example  of  white  rust  is  the  one  on 
cruciferous  plants  like  the  mustard,  turnip,  cabbage  and  shep- 
herd's purse.  This  white  rust  (Cystopus  candidus  =  Albugo 


FUNGI,    WHITE   RUST 


259 


Fig.  218. 
Ripe  oospore  of  Peronospora  alsinearum. 


Candida)  is  very  common  on  the  shepherd's  purse,  deforming  the 
stems,  leaves,  flowers,  and  fruit.  The  mycelium  is  intercellular, 
and  branched  haustoria 
penetrate  the  cells. 

419.  Asexual  stage. — 
The  sporophores  are  short, 
are    developed   in  great 
numbers,  and  crowded  un- 
derneath    the     epidermis. 
These     sporophores    bear 
chains  of  spores  (conidia; 
fig.    219),    and    the    mass 
bursts    through    the    epi- 
dermis,   giving    a    white 
rusty     appearance.       The 
spores    germinate    by   the 

formation  of  zoospores  as  in  the  grape  downy  mildew. 

420.  Sexual  reproduction. — This  process  is  very  much  as 
described  for  the  downy  mildews,  but  in  some  species  many  sperm 

nuclei  from   the  sperm 
case  enter  the  egg  and 
pair  off  to  fuse  with  the 
many  nuclei  in  the  egg. 
431.  Formula*  for 
the    life     history    of 
the   water   molds    and 
downy  mildews.      This 
Fig  2I9>  can   be  written   as  fol- 

From    Cystopus  candidus,  conidial   stage.     A,  tuft  of  loWS.    Starting    with    the 
conidiophores  sprus,   showing  a  few  conidia  in  chains; 

B,  conidia  forming  swarm  spores  or  zoospores;  C,  zoo-  fertilized      GS.2'.      Fertil- 
spores,  some  of  them  germinating;  D,  germinating  zoo- 
spores,   the    hyphae   about   to   enter   stoma.     (After   De  ized  Cfiffif  —  Plant — aSCX- 
Bary.) 

ual     spores    repeatedly 


formed 


\ 


sperm  gamete 
egg  gamete 


fertilized  egg,  etc.,  and  can  be  ab- 


*  Not  to  be  memorized.     Introduced  to  represent  graphically  the  life 
cycle. 


260  GENERAL   MORPHOLOGY   OF   PLANTS 


\ 


breviated  as  follows:  FE —  P — asp  —  P  —  asp — P  \      /  FE,  etc. 

In  some  of  the  blights  and  downy  mildews  zoospores  are  pro- 
duced on  the  germination  of  the  fertilized  egg.  The  formula  for 
these  could  be  written  as  follows:  FE — sp — P — asp — P — asp — 

P  <^  y  FE,  etc.  If  g  is  allowed  to  stand  for  each  of  the  gametes, 
the  formula  could  be  written  as  follows:  FE — sp — P — asp — 
P —  x  ^FE,  etc.  Various  methods  can  be  devised  to  repre- 

o 

sent  the  life  history. 


CHAPTER   XXVII. 
FUNGI    (Continued). 

THE  SAC  FUNGI,  OR  ASCUS   FUNGI. 
(Class  Ascomycetes.) 

422.  General  characters. — The  mycelium  is  septate,  and 
grows  either  within  the  substratum  or  upon  the  surface.  In  the 
latter  case  it  often  sends  branches,  called  haustoria,  into  the  cells 
of  the  host,  to  obtain  nutriment.  Many  of  the  species  are  poly- 


Fig.  220. 

A,  a  perfect  fungus  (Cordyceps  militaris)  parasitic  on  pupa  of  a  moth.  Head  por- 
tion of  the  fungus  enlarged,  showing  fruit  bodies  (perithecia)  containing  asci  and  spores. 
B,  an  imperfect  stage  showing  conidiophores  bearing  white  masses  of  conidia. 

morphic,  i.e.,  different  stages  in  the  life  history  of  the  same  species 
appear  under  different  forms.  Some  of  these  forms  are  asexual 
stages  and  bear  conidia  (asexual  spores)  which  serve  to  multiply 

261 


262  GENERAL   MORPHOLOGY   OF  PLANTS 

and  propagate  the  fungus  rapidly.  These  stages  are  called  im- 
perfect. Another  stage,  which  is  the  final  stage  in  the  life  history, 
or  life  cycle,  bears  the  sacs  or  asci  (containing  the  spores  or  asco- 
spores)  which  make  the  characteristic  fruit  form  of  the  members 
of  the  class.  This  stage  is  called  the  perfect  stage  of  the  fungus. 
It  is  often  developed  as  the  result  of  a  sexual  act,  and  thus  repre- 
sents the  sexual  reproduction  in  the  class.  Many  of  the  species, 
however,  are  believed  to  have  lost  the  function  of  sexuality  and  are 
supposed  to  develop  the  asci  independently  of  a  true  fertilization. 
In  a  few  of  the  simple  forms  the  asci  are  scattered  without  order  in 
loose  wefts  or  knots  of  mycelium.  In  the  majority  of  the  species 
the  asci  are  closely  crowded  into  extended  surfaces  (forming  a 
fruiting  surface,  the  hymenium)  or  grouped  in  cup-shaped  or 
globose  fruit  bodies  partly  or  entirely  surrounded  by  a  special 
fungus  tissue  (a poth'ecium) ,  or  entirely  surrounded  by  fungus 
tissue  (perithecium} .*  In  some  species,  the  lichen  fungi,  the 
plant  body  is  made  up  of  an  intimate  association  of  fungus 

mycelium  and  algal  cells. 

423.  The  powdery  mildews 
(Perisporiales). — The  powdery 
mildews  are  very  common  and 
conspicuous  fungi  parasitic  upon 

To  THE  TEACHER.  The  practical 
study  should  include  at  least  one  of 
the  powdery  mildews.  There  are  other 
members  of  the  sac  fungi  which  make 
striking  examples  for  illustration.  These 
can  be  shown  by  the  teacher,  and  at 
his  discretion  may  be  included  in  the 
practical  study  where  the  time  de- 
voted to  the  course  will  permit.  One 
lichen  can  be  studied  and  others  com- 

Fig.  221.      ^  oared.      The  yeast  should   be  studied 

Leaves  of  willow,  showing  willow  mil-      *****  J 

dew.  The  black  dots  are  the  iruit  bodies  unless  this  has  already  been  done 
(.pei  ithecla)  seated  on  the  white  mycelium.  .  T 

in  Part  I. 

*  These  fruit  bodies  of  the  Ascomycetes  are  sometimes  called  ascocarps, 
i.e.,  sac  fruits. 


FUNGI:  SAC  FUNGI  263 

a  great  variety  of  plants,  on  leaves,  stems,  flowers,  and  fruit. 
Many  of  the  common  mildews  belong  here.  The  mycelium  grows 
on  the  surface  of  the  host,  forming  a  thin  and  irregular  web-like 
whitish  layer,  just  visible  to  the  eye.  Branches  called  haustoria 
penetrate  to  the  epidermal  cells,  in  some  species  even  to  the  deeper 
cells,  and  draw  nutriment  from  the  protoplasm.  When  very 
young  leaves  and  stems  are  affected  they  are  often  checked  in 
growth.  The  large  number  of  white  conidia  (or  conidia-spores)  in 
chains  or  in  loose  masses  give  a  powdery  appearance  to  the  sur- 
face of  the  plants  affected,  hence  the  name  powdery  mildews. 
Some  of  the  important  diseases  caused  by  the  powdery  mildews  are 
the  gooseberry  mildew;  the  cherry  mildew,  growing  on  cherry, 
peach,  and  apple  trees,  especially  injurious  to  nursery  stock;  the 
rose  mildew,  lilac  mildew,  etc. 

Lilac  Mildew  (Microsphcera  Alni). 

424.  The  conidial  stage. — This  is  developed  in  asexual  repro- 
duction.    Short  erect  branches  arise  from  the  superficial  mycelium 
which  are  divided  by  cross  walls  into  short  cells.     The  branches 
grow  at  the  base  and  continue  to  divide  into  short  cells,  raising 
the  older  cells  farther  and  farther  away  from  the  surface.     At  the 
same  time  the  older  cells  swell  out  somewhat  so  that  they  appear 
like  chains  of  beads,  or  small  barrel-shaped  spores  or  conidia. 
The  older  ones  separate  and  fall  upon  the  surface  of  the  leaf  or 
stem,   etc.,   giving  a  powdery   appearance.     These   conidia  are 
carried  to  other  plants  or  other  parts  of  the  same  plant,  there 
spreading  the  disease. 

425.  The  ascus  stage,  or  perfect  stage. — This  is  developed 
after  the  formation  of  conidia  as  the  result  of  a  sexual  process 
ending  in  the  formation  of  minute  brown  or  blackish  fruit  bodies,* 
a  cellular  structure  formed  of  septate  threads  which  envelop  the 
developing  asci.     These  fruit  bodies  are  often  very  numerous, 
appearing  as  minute  black  specks  just  visible  to  the  eye.     The 
fruit  body  is  provided  with  appendages  of  a  dark  color,  consisting 

*  Called  here  a  perithecium. 


264 


GENERAL   MORPHOLOGY   OF  PLANTS 


of  short  septate  hyphae  which  are  branched  at  the  end  several 
times  in  a  forked  manner  (fig.  224).     The  sacs  or  asci  are  some- 


Fig.  223. 


Fig.    222. 

Willow  mildew;  Fruit  of    willow    mildew,    showing   hooked 

bit    of     mycelium  appendages.     Genus  Uncinula. 

with     erect    comdio-  other    mildew 

phores     bearing  Figs.   223,   224.  —  Perithecia   (perithecium)     c 

chains     of     conidui;  of  two   powdery  mildews,  showing  escape  of    P?n     £e?' 

left  asci   containing  the   spores  from  the  crushed    Microsphaera. 


Fig.  224. 

Fruit  body  of   an- 
"th 


conidium      at 
germinating. 


fruit  bodies. 


what  elliptical  in  outline.  Several  are  formed  in  each  fruit  body, 
and  may  be  seen  by  crushing  the  latter  in  water  and  examin- 
ing with  a  microscope.  Each  ascus  contains  several  spores. 
Other  genera  of  the  powdery  mildews  have  different  kinds  of 
appendages. 

426.  The  sexual  process  in  the  powdery  mildews.  —  The 
sexual  organs  are  short  branches  of  the  mycelium,  a  sperm  case 
and  an  egg  case.  The  processes  here  described  occur  in  the 
genus  Sph&rotheca.  These  branches  arise  close  together  and 
their  ends  come  in  contact.  At  the  point  of  contact  an  opening 
is  dissolved  through  the  walls.  The  sperm  nucleus  in  the  sperm 
case  moves  into  the  egg  case  and  fuses  with  the  egg  nucleus  (figs. 
225-226).  The  egg-case  cell  now  grows  .into  a  short  branch  of 
five  or  six  cells.  In  the  last  cell  but  one  are  two  nuclei.  These 
fuse  into  one,  and  the  cell  grows  out  into  a  large  globose  cell,  the 
ascus.  The  nucleus  now  divides  to  form  eight  nuclei  which 


FUNGI:  SAC  FUNGI 


26S 


become   centers  in  the   protoplasm  for  the   formation  of  eight 
ascospores. 


Fig.  225. 

Contact  of  antheridium 
and  carpogonium  (car- 
pogonium the  larger 
cell);  beginning  of  fertili- 
zation. 


Fig.  226. 

Disappearance  of  con- 
tact walls  of  antheri- 
dium and  carpogonium, 
and  fusion  of  the  two 
nuclei. 


Fig.  227. 

Fertilized  egg  sur- 
rounded by  the  envelop- 
ing threads  which  grow 
up  around  it. 


Figs.  225-227.  —  Fertilization  in  Sphaerotheca;  one  of  the  powdery  mildews.     (After 
Harper.) 

427.  The  black  fungi  (Sphaeriales). — The  black  fungi 
include  a  vast  number  of  the  sac  fungi,  with  many  genera  and 
species.  The  fruit  bodies  (perithecia) 
are  black  or  dark  brown;  they  occur 
singly,  in-  troops  or  in  masses,  and 
sometimes  are  imbedded  in  a  black 
stroma  (a  compact  sterile  fungus 
tissue).  Many  are  saprophytes  and 
many  others  are  parasites  on  other 
plants,  causing  leaf  spots,  blights, 
rots,  cankers,  knots,  etc.  Many  of 
these  produce  serious  diseases  of 
vegetables,  farm  crops,  orchard  and 
forest  trees.  Many  of  them  have 
"  imperfect  "  stages  on  which  asexual 
spores  (called  conidia)  are  borne  on 
free  hyphae  of  a  great  variety  of  form  Fis- 228- 

.      .  .  Black  knot  of  plum  (Plowrightia 

and     association,    or    in     Other     Cases      morbosa),  showing  deformities  of  the 

stems. 

the  asexual  spores  are  borne  on  snort 

hyphse  enclosed  in  bottle-shaped  or  oval  cases   resembling  the 

sac  fruit  bodies.     The  perfect  stage  is  represented  by  the  true  sac 


266 


GENERAL   MORPHOLOGY   OF  PLANTS 


fruits,  or  fruit  bodies,  containing  the  sacs  or   asci,   the  greater 
number  of  the  species  having  sacs  each  containing  eight  spores. 

428.  Examples  of  the  black  fungi. — A  few  only  are  briefly 
mentioned  here.  The  black  knot  of  plum  and  cherry  (Plowrightia 
morbosa  or  Otthia  morbosa).  This  produces  black  rough  excres- 
cences on  the  limbs  of  living  cherry  and  plum  trees,  which  spread 
from  year  to  year,  finally  encircling  the  limbs  and  killing  them. 


Fig.  229. 


Plowrightia  morbosa,  showing  details  of  the  fungus  which  causes  the  galls.  A,  section 
through  the  velvety  stroma.  showing  conidia  bearing  stroma.  B,  conidiophores  and  conidia 
still  more  enlarged.  C,  a  single  perithecium  containing  asci  and  paraphyses.  D,  paraphyses 
and  asci  containing  spores  still  more  enlarged.  E,  ascospores,  one  germinating.  (After  Farlow.) 

When  a  tree  is  badly  infected  it  is  an  ugly  sight.  In  early  summer 
the  knots  are  covered  with  a  black  velvety  growth  of  short  erect 
hyphae  bearing  the  conidia.  During  the  winter  the  sac  fruits  are 
formed,  and  are  thickly  crowded  over  the  surface  of  the  knot, 
the  spores  ripening  along  in  February.  These  knots  should  be 
cut  out  and  burned,  or  badly  infested  trees  removed  and  all  dis- 
eased branches  burned. 

429.  The  cup  fungi. — These  include  a  large  number  of  sac 
fungi  which  are  mostly  saprophytic,  and  grow  on  the  ground, 
rotten  and  dead  wood,  leaves,  etc.  Many  of  these  belong  to  the 
old  genus  Peziza.  The  asci  are  crowded  over  the  upper  surface 
of  the  cup,  and  surrounded  below  and  on  the  sides  by  the  sterile 


FUNGI:  SAC  FUNGI 


267 


Fig.  230. 

Plum  rot  (Sclerotina  fructigena),  showing  the  conidial  stage  (Monilia  fructigena)  of  the 
fungus,  on  the  surface  of  the  plums,  which  causes  the  rot.     Natural  size. 


tissue  of  the  fruit  body  or  ascoma. 
the  most  injurious  (Scler- 
otinia  fructigena)  causes 
the  common  brown  rot 
of  cherries,  plums, 
peaches,  and  sometimes 
of  apples  also.  The 
asexual  stage  (Monilia) 
causes  the  rot  of  the 
fruit.  The  conidia  are 
borne  in  long  chains. 
The  rotted  peaches  and 
plums  become  dried  and 
"  mummified,"  and  many 
hang  on  the  trees  for  a 
large  part  of  the  winter 
and  the  following  sum- 
mer. They  fall  to  the 


A  few  are  parasitic.     One  of 


Fig.  231. 


c.  Monilia   fructigena,    showing    chains  of  conidia,    also 

ground,    and   after  paSS-     showing  how  the  conidia  separate  from  each  other  in 

ing  another  winter,  half   the  chains"   Two  conidia  a 


268  GENERAL   MORPHOLOGY   OF   PLANTS 

or  completely  buried  in  the  ground,  the  dormant  mycelium  in 
the  "  mummies  "  develops  the  cups,  which  are  supported  on 
long  stalks  to  lift  them  above  the  ground. 


Fig.  232. 

Sclerotina  fructigena,  the  trumpet-shaped  fruit  bodies  growing  from  old  peach  mummies 
which  were  affected  with  the  rot.     Natural  size. 

430.  The   morels. — These  are  large  fleshy  fungi  with  a  stout 
stalk  bearing  a  large  head  which  is  covered  with  numerous  shallow 
depressions  separated  by  ridges.     The  entire  surface  of  the  head 
is   covered   with   the    asci    intermingled   with   numerous   sterile 
hyphae  (paraphyses).     The   morels  (Morchella)  appear  in  damp 
places  in  early  spring  and  are  prized  as  edible  fungi.     They  are 

•sometimes  called  mushrooms,   but  do   not  belong  to  the  true 
mushroom  group. 

431.  The  yeast  fungi. — The  yeast  fungi,  or  sprouting  fungi,  as 
they  are  often  called,  are  by  some  classed  among  the  sac  fungi  as 
degenerate  forms.     The  yeast  plant  is  remarkable  for  its  activity 
in  producing  fermentation  especially  of  solutions  containing  sugar 
(see  paragraph  192  for  fermentation  by  yeast),  giving  off  CO2  and 
forming,    alcohol;   one   yeast  (Saccharomyces  cerivisece)   is  used 
both  in  bread-rising  and  in  brewing  beer.     The  yeasts  usually 
consist  of  single  cells,  oval  or  elliptical  in  form,  and  in  this  con- 
dition they  are  single-celled  plants.     They  multiply  by  a  process 
of  budding  or  sprouting.     Near  each  end  of  a  cell  a  small  bud 
appears  which  has  only  a  frail  connection  with  the  parent  yeast  cell. 
This  bud  increases  in  size,  and  soon  separates,  forming  a  new  yeast 
plant.     Sometimes  these  buds  remain  connected  for  a  time,  form- 
ing small  colonies,  which  soon  separate  into  the  separate  cells  if 


FUNGI:   SAC  FUNGI 


269 


disturbed.     When  the  air  is  largely  excluded  from  sugar  solu- 
tions in  which  the  yeast  is  growing,  fermentation  goes  on  rapidly 


Edible  Morel.    Morchella  esculenta.    The  asci,  forming  hymenium,  cover  the  pitted  surface. 

and  the  growth  and  multiplication  are  retarded.  With  the  intro- 
duction of  more  air  fermentation  is  retarded,  while  growth  and 
multiplication  are  accelerated.  Under  proper  conditions  of  tem- 
perature and  with  very  free  access  of  air,  spore  formation  takes 


2/O  GENERAL   MORPHOLOGY   OF   PLANTS 

place.  The  protoplasm  in  a  yeast  cell  condenses  into  three  or 
four  small  globose  shining  bodies  which  are  retained  in  the  yeast 
cell,  the  nucleus  having  previously  been  divided  into  four  nuclei. 
The  yeast  cell  with  the  enclosed  spores  is  regarded  as  an  ascus. 
The  yeast  plant,  however,  is  supposed  to  be  a  degenerate  form, 
for  some  of  the  other  sac  .fungi  as  well  as  some  of  the  spore-case 
fungi  (or  alga-like  fungi)  under  certain  conditions  degenerate  into 
yeast  forms.  No  one,  however,  has  ever  succeeded  in  changing 
the  true  yeasts  into  any  of  these  better  organized  forms,  though 
some  yeasts  form  a  temporary  mycelium  which  later  breaks  up 
into  yeast  cells.  The  yeast  used  in  bread  "  rising  "  and  in  brewing 
beer  is  now  a  domestic  or  industrial  form.  There  are,  however, 
many  wild  yeasts,  which  are  abundant  on  all  sorts  of  vegetables 
and  multiply  in  decaying  parts.  Some  of  these  wild  yeasts  are 
associated  with  certain  bacteria,  forming  little  nodules  which  have 
been  used  by  natives  of  certain  countries  in  making  fermented 
drinks,  as  "  ginger  beer  "  from  the  "  ginger- beer  "  plant,  or 
"  kumiss  "  from  mare's  milk  fermented  by  throwing  in  some  of 
these  grains,  which  is  used  by  some  of  the  tribes  of  the  Caucasus. 

The  Lichens. 

432.  Nature  of  lichens. — The  lichens  are  curious  structures 
composed  of  the  elements  of  two  different  kinds  of  plants,  a  fungus 
and  an  alga.  The  plant  body  of  the  lichen  is  made  up  of  fungus 
threads  in  the  meshes  of  which  the  algae  are  enclosed.  Many  of 
the  lichens  are  greenish  in  color,  this  color  being  imparted  to  the 
lichen  thallus  by  the  algal  cells  underneath  the  outer  layer  of 
fungus  threads.  Others  are  brown,  reddish,  etc.  Their  method 
of  nutrition  is  interesting  and  illustrates  one  of  the  forms  of 
symbiosis  (paragraph  206).  The  algal  cells  perform  the  function 
of  photosynthesis,  so  that  the  fungus  element  as  well  as  the  algal 
is  provided  with  the  necessary  carbohydrates.  The  fungus  is 
thus  entirely  dependent  on  the  alga  for  its  organic  or  carbohydrate 
food.  On  the  other  hand  the  fungus,  being  external  in  most  cases, 
and  forming  the  "  rhizoids  "  and  holdfasts,  supplies  the  solution 


FUNGI:    THE  LICHENS 


271 


of  mineral  and  nitrogenous  substances,  protects  the  alga  during 
dry  seasons  and  holds  it  in  place  on  steep  slopes.     Many  lichens 


Fig.  234. 
Foliaceous  lichen  (Physcia  stellaris).     Natural  size. 

are  multiplied  and  propagated  naturally  by  small  specialized 
bits  of  the  lichen  thallus  (soredia) 
which  become  separated  from  the 
main  body.  The  fruiting  stage, 
however,  is  that  of  the  fungus. 
The  fruit  of  the  perfect  stage  in 
nearly  all  of  the  lichens  is  that  of 
the  sac  fungi  with  which  they  are 
classed.  There  are  a  few  tropical 
forms  with  basidium  fruit  fungi.  A 
large  number  of  the  lichen  sac  fungi 
have  fruit  bodies  like  those  of  the 
black  fungi,  while  in  many  others  they 
are  like  the  cup  fungi.  Other  pecul- 
iarities of  the  lichens  can  be  noted 
after  the  study  of  a  few  forms. 

433.  The  foliaceous  lichens.— These  are  leaf-like,  and  grow 
on  rocks,  fences,  tree  trunks,  or  on  the  ground,  where  they  are  more 


Fig.  235. 

Much  enlarged  section  of  portion 
of  lining  layer,  showing  the  asci  (i, 
2,  3,  4)  with  their  contained  spores. 
(After  Sachs.) 


272 


GENERAL   MORPHOLOGY   OF  PLANTS 


or  less  loosely  attached.  A  common  one  on  board  and  rail  fences 
as  well  as  on  other  woody  structures  is  the  star-shaped  Physcia 
(Physcia  stellaris).  The  plant  is  circular,  rather  closely  appressed 
to  the  wood,  and  the  margin  is  radiately  divided  into  narrow 
irregular  lobes,  giving  it  a  star-shaped  form.  It  is  dull  gray  in 
color.  Scattered  over  the  central  portion  are  a  number  of  cup- 
shaped  or  saucer-shaped  bodies,  the  fruit  bodies,  or  the  apothecia, 
as  they  are  called  in  the  lichens.  This  fruit  body  is  like  that  of  the 
cup  fungi.  The  sacs  or  asci  are  mingled  with  numerous  sterile 
hyphae  (paraphyses)  which  overtop  the  asci  and  broaden  out,  thus 
forming  a  covering  (epithecium)  over  the  ends  of  the  asci.*  Par- 
melia  is  another  very  common  foliaceous  lichen  growing  on  rocks, 
sometimes  very  common  on  small  stones  in  the  field.  Peltigera 
is  a  common  one  growing  on  leaf  mold  in  the  forest. 

434.  The  fruticose  lichens. — These   are  more  or  less  erect 
forms  and  often  very  much  branched.     Some  species  of  Cladonia 

grow  on  rotting  wood,  and 
one  species  with  bright  red 
rounded  tops  is  very  com- 
mon on  rotten  stumps  and 
logs.  The  bright  red  bodies 
are  the  fruit  bodies  (apo- 
thecia), which  here  are 
arched  instead  of  cup- 
shaped.  Another  species 
of  Cladonia  (C.  rangiferina) 
is  the  reindeer  moss.  It 
profusely  branched 


Fig.  236. 

Fruticose  lichen  (Cladonia  cristatella),  thallus 
grayish  green,  the  tips  bright  red.  Grows  on 
rotten  logs,  etc.  Natural  size. 


IS 


into  slender  grayish  green 
branches.  It  is  very  com- 
mon on  the  ground  of  the  arctic  tundra,  sometimes  covering 
extensive  areas.  It  is  eaten  by  the  reindeers.  Another  common 

*  The  fruit  body  of  the  lichen  is  the  ascoma.  The  sterile  wall  outside  of  the 
group  of  asci  is  the  excipulum;  the  broadened  ends  of  paraphy  ses  united  above 
the  asci  form  the  epithecium;  the  tissue  beneath  the  asci  is  the  hypothecium. 


FUNGI:    THE  LICHENS 


2/3 


fruticose  lichen  is  the  " hanging  moss" 
of  the  Northern  States  (Usnea  barbata), 
often  found  hanging  from  the  limbs  of 
trees  in  damp  or  swampy  woods.     It 
consists  of  very  fine,   grayish,  much- 
branched  threads,   sometimes  reaching  a  length   20 
cm.  to  30  cm.  or  more,  but  usually  smaller:    It  should 
not  be  confused  with  the  "  hanging  moss  "  (Tilland- 
sia]   of   the   Southern   States,  which   is   a   flowering 
plant. 

435.  Crustaceous  lichens. — These  form  thin  and 
very  close  incrustations  on  rocks  and  the  trunks  of 
trees.     They  are  often  so  closely  connected  with  the 
rock  or  bark  that  it  looks  as  if  the  latter  were  merely 
painted.     The  minute  fruit  bodies  are  scattered  over 
the  surface.      The  trunks  of  young  beech  or  birch 
trees    are    sometimes   nearly   covered  with    different 
species  of  various  colors. 

436.  The    gelatinous    lichens. — In    the    above 
three  types  of  lichens  the  fruit  bcdy  is  stratified,  the 
algae  being  in    a   layer   a    short   distance   below  the 
upper  surface.    The  algae  present  are  usually  isolated 
cells  resembling  the  alga  Pleiirococcus.     In  the  gelat- 

Fig.  237.  inous  lichens  the  algal  element  is  more  evenly  mixed 
nea  barbata),  with  the  fungus  element.  The  algae  here  are  often 

often     called  .          ._T  -,    77 

hanging  moss,    of   the   Nostoc  type.     Calluna  is  an  example. 

437.  The  work  of  lichens  in  soil  building. — The  lichens  are 
believed  to  be  among  the  most  important  early  agencies  in  soil 
making.  Growing  as  many  of  them  do  on  bare  rocks  where 
scarcely  any  other  vegetation  can  hold,  especially  on  sloping  sur- 
faces, their  disintegrating  bodies  mingle  with  the  finely  weathered 
and  disintegrated  rock  which  lodges  in  crevices.  Here  many 
ferns,  grasses,  and  other  plants  can  find  a  foothold  and  obtain 
nourishment.  The  algae  can  also  grow  on  moist  rocks,  but  are 
killed  when  long  exposed  to  dry  air  in  these  situations.  But  when 
the  alga  is  surrounded  by  the  close  mat  of  fungus  elements  in  the 


2/4 


GENERAL   MORPHOLOGY   OF   PLANTS 


lichen  body  it  is  prevented  from  injurious  desiccation  and  is  held 
on  even  to  steep  slopes  or  perpendicular  rock  faces. 

438.  The  relation  of  the  algae  and  fungus  in  the  lichen 
thallus. — In  the  early  history  of  the  study  of  lichens  it  was  thought 
by  some  that  the  lichen  was  an  individual  plant  (autonomous 
plant),  and  that  the  algal  cells  were  special  spores  (gonidia) 
which  were  cut  off  from  the  colorless  threads  of  the  mycelium. 


Lichen  tundra,  showing  the  "reindeer  moss"  or  lichen,  Alaska.     (Copyright  by  E.  H. 
Harriman.) 

Opposed  to  this  theory  another  one  came  to  be  accepted  by  some 
students,  i.e.,  that  the  alga  and  the  fungus  are  distinct  plants,  and 
this  theory  has  finally  prevailed.  The  most  important  arguments 
presented  for  this  theory  were  furnished  by  some  investigators 
who  separated  the  spores  of  the  lichen  and  grew  them  free  from  the 
algae,  and  also  separated  the  algal  cells  and  grew  them  as  separate 
algae.  In  this  way  it  has  been  possible  to  identify  some  of  the  algae 
with  those  which  are  found  in  a  free  state.  Pleurococcus  vulgaris, 
so  common  in  cool  shady  places,  is  one  of  these.  The  blue-green 


FUNGI:    THE  LICHENS 

alga  Nostoc,  with  cells  like  a  chain  of  beads,  has  been  found  to  be 
a  component  of  many  of  the  gelatinous  lichens.  When  the  spores 
of  these  lichens  are  germinated  in  the  presence  of  these  algae,  the 
mycelial  threads  coil  around  the  algae,  envelop  them,  and  finally 
a  complete  lichen  thallus  is  developed  which  ultimately  bears  the 
fruit  bodies  and  asci. 

439.  Uses  of  lichens. — As  mentioned  above,  the  "reindeer  moss" 
in  the  arctic  regions  is  eaten  by  the  reindeer.     In  lower  latitudes 
where  it  is  abundant  it  is  often  used  as  packing  material  to  protect 
furniture   or   frangible   wares.     Some   arctic   lichens    (Cetraria), 
called  "  Iceland  moss,"  are  used  for  food  by  grinding  them  and  mix- 
ing them  with  ground  wheat.     Others  which  contain  purple  or 
blue  or  crimson  pigments  are  used  for  making  dyes  called  "  archil," 
also  orchil  or  cudbear.     This  lichen  (Roccella  tinctoria]  grows  on 
rocks  in  the  Canary  and  Cape  Verde  Islands.     Litmus  paper  is 
made  from  the  litmus  dye  prepared  by  treating  orchil  with  soda 
or  potash. 

440.  The  life  history  of  the  sac  fungi  which  produce  the  fruit 
bodies  (perithecia,  or  ascocarps,  a  more  general  term)  as  a  result 
of  a  sexual  act  can  be  represented  as  follows,  starting  with  the 
mycelium  as  the  plant.    Plant  —  asexual  spores  —  Plant  —  asexual 

spores  —  Plant  —  ^  /  ascocarp — ascospore — Plant, 

etc. ,  abbreviated  as  follows :  P  —  asp  —  P  —  asp  —  P  ^  ^  ^>  asc  — 

sp  —  P,  etc.  Where  the  asexual  spores  are  not  formed  in  the  life 
history  they  would  be  omitted  from  the  formula. 


CHAPTER  XXVIII. 
FUNGI    (Continued). 

THE   BASIDIUM  FUNGI  (CLASS   BASIDIOMYCETES). 
The  Smuts* 

441.  General  characters. — The  smuts  are  a  group  of  fungi 
parasitic  chiefly  on  the  flowering  plants.     The  mycelium  lives  in 
the  interior  of  its  host.     The  spores  have  usually  rather  thick 
brown  walls,  and  are  usually  produced  in  great  masses  in  the 
fruiting  part  or  stems  of  the  host,  after  the  mycelium  has  con- 
sumed these  parts.     These  masses  break  down  into  a  fine  dark 
powder  mixed  with  the  minute  dark  spores,  which  gives  a  smutted 
appearance  to  the  affected  parts  of  the  host. 

442.  The  corn  smut.f — The  corn  smut  (Ustilago  zecR]  is  one 
of  the  most  common   and   conspicuous    species   of   the    smuts. 
Nearly  every  field  of  Indian  corn  shows  a  number  of  examples  and 
often  many  plants  are  affected.     It  forms  large  excrescences  on  the 
ears,  the  tassel,  the  joints  of  the  stem,  and  even  on  the  leaves. 
These  are  at  first  whitish,  but  later  become  black  as  the  spores 
ripen.     The  masses  of  smut  then  are  often  very  large.     The  spores 
in  this  smut-mass  are  rounded,  minute,  spiny  bodies.     When  these 
spores  germinate  a  short  hypha  or  germ  tube  is  formed  which  has 
a  few  cross  walls.     Small  elongated  spores  are  formed  on  the  sides 
of  this  hypha  (called  here  a  promycelium)  near  the  joints  or  cross 
walls.     These    are    called   sporidia.     When    these    sporidia   fall 

*  The  smuts  are  not  true  basidiomycetes.  The  promycelium  formed  by 
the  germination  of  the  smut  spore  is  believed  by  some  to  be  an  elementary, 
or  "  beginning,"  basidium.  If  so,  the  smuts  would  belong  to  the  basidium 
series  representing  very  low  forms  of  the  same. 

f  To  THE  TEACHER.  The  corn  smut  may  be  used  for  the  practical 
work  and  others  may  be  introduced  for  comparison. 

276 


FUNGI:    THE   SMUT   FUNGI 


277 


Fig.  239. 

Corn     smut     (Ustilago     zeae), 
affected  e»r,  stalk,  and  blades. 


down  between  the  young  blades  at  the  end  of  a  growing  corn  stalk 
they  germinate,  producing  a  germ  tube  which  enters  the  tissues  of 
the  corn  plant  and  about  six  or  eight 
weeks  later  produces  the  smut  masses 
again.  The  infection  is  local  in  the 
case  of  the  corn  smut,  any  of  the  em- 
bryonic tissues  of  the  corn  being  sus- 
ceptible if  the  germinating  sporidia  are 
present.  The  infection  which  produces 
the  smut  at  the  lower  joints  of  the 
stalk  takes  place  earlier  than  that  in 
the  ear  or  that  on  the  tassel.  The  corn 
smut  is  often  relished  by  cattle,  and 
does  not  seem  to  injure  them  unless 
they  eat  too  great  a  quantity. 

443.  Other  species  of  smut. — 
Other  examples  of  smut  are  the 
loose  smuts  on  the  grains,  as  the  loose  smut  of  oats  (U.  avence), 
the  loose  smut  of  wheat  (U.  tritici),  and  the  loose  smut  of  barley 
(U.  hordei).  The  only  part  of  the  host  injured  is  the  flower,  the 
young  kernels  (ovary)  and  parts  of  the  palets  being  reduced  to  a 
black  smutty  mass  con- 
sisting of  disintegrated 
parts  of  the  flower,  the 
mycelium,  and  the 
spores.  They  are  called 
loose  smuts  because  the 
mass  of  spores  not  being 
covered,  even  by  any  Fig.  24o. 

rlpliVatA  m^mhrariA  tliA  Corn  smut,  spore  germinating  and  producing  sporidia. 
delicate  memDrane,  tne  At  the  right.  sporidia  budding  and  producing  secondary 

spores  are    easily  scat-    sporidia'    (Afte 

tered.  Although  only  the  flower  parts  are  injured,  the  mycelium 
travels  all  through  the  host  while  it  is  growing,  from  the  seedling  up 
to  the  full-grown  plant.  The  method  of  infection  is  very  interesting. 
In  the  case  of  the  oat  plant  the  smut  spores  clinging  to  the  seed  oats 
germinate  at  the  same  time  that  the  oat  grains  do.  The  sporidia 


GENERAL   MORPHOLOGY   OF  PLANTS 


formed  on  the  pro  mycelium  germinate  and  the  germ  tube  enters  the 
oat  seedling  at  the  base  of  the  first  leaf  sheath.  In  the  case  of  the 
loose  smut  of  wheat  and  barley  the  method  of  infection  is  different. 
At  the  time  the  wheat  or  barley  is  in  flower,  the  smut  on  the  affected 
plants  in  the  field  is  just  ripening,  and  spores  are  blown  from  the 
smutted  heads  to  the  open  flowers  of  healthy  plants.  The  spores 
lodge  on  the  feathery  style  of  the  flower  and  germinate.  They  do 


( 


Fig.  241. 

Loose    smut    of    barley    (Ustilago 
nuda).     %  diameter. 


Fig.  242. 

Bunt  or  stinking  smut  of  wheat 
(Tilletia  tritici).  Note  the  flaring 
position  of  the  palse. 


not  produce  a  promycelium,  but  the  germ  tube  of  the  spore  enters 
directly  into  the  style,  and  passes  down  into  the  ovary,  where  it 
forms  a  small  amount  of  dormant  mycelium  which,  however,  does 
not  injure  the  grain,  so  that  it  ripens  with  the  dormant  mycelium 
of  the  smut  imprisoned.  When  these  grains  of  wheat  are  sown, 
the  dormant  mycelium  begins  to  grow  as  the  seed  germinates, 
and  passes  through  the  scutellum  into  the  shoot.  It  then  con- 
tinues to  grow  along  with  its  host,  as  in  the  case  of  the  oat  smut. 
Beside  the  loose  smut  of  barley  there  is  another,  the  covered  smut, 


FUNGI:    THE   RUST  FUNGI 


2/9 


so  called  because  there  is  a  thin  membrane,  the  remnant  of  the 
palets,  which  covers  the  mass  of  smut,  so  that  it  does  not  so  readily 
scatter.     There  is  also  another  kind  of  wheat  smut,  the  stinking 
smut  (two  species),  so  called  because 
of  its  foul  odor.     This  smut  injures 
only  the  interior  of  the  wheat  grain, 
which  it  changes  to  a  greasy  mass  of 
black    smut    spores    covered    by    the 
uninjured  seed  coats  and  ovary  wall. 
The  grains  have  the   appearance    ex- 
ternally of  being  perfectly  sound,  but 
they  are  somewhat   stouter   than   the 
normal  grains.     Infection  takes  place 
as  in  the  case   of  the  oat  smut,  but 
the  promycelium   of   the   germinating 
spore  is  undivided,  and  the   sporidia, 
which   are   narrow,  long,  and  slightly  ary  spores- 
curved,  are  borne  in  a  cluster  at  its  apex. 

444.  Treatment  for  the  prevention  of  smut. — To  prevent 
the  loose  smuts  of  wheat  and  barley,  seed  should  be  selected  from 
fields  free  from  smut.  Oat  smut  and  the  stinking  smut  of  wheat 
can  largely  be  prevented  by  treating  the  seed  wheat  with  formalin, 
or  by  a  solution  of  copper  sulphate,  or  by  hot  water  (at  i28°-i32°  F. 
for  a  few  minutes).  In  the  case  of  corn  smut  infected  stalks 
should  be  cut  out  and  destroyed  before  the  smut  masses  ripen. 


Fig.  243. 
Spores  of  "bunt,"    or    "stinking 


Rust  Fungi  (Uredinales)* 

445.  The  rust  fungi. — There  are  a  large  number  of  species  of 
rust  fungi  on  grasses,  cereals,  herbs,  trees,  and  ferns.  All  of 
them  are  parasites,  and  some  cause  great  injury  and  loss.  The 
loss  to  the  wheat  crop  in  the- United  States  is  estimated  variously 
from  $20,000,000  to  $60,000,000  annually.  The  yellowish  or 
blackish  spore  masses,  often  thickly  scattered  over  parts  of  the 


*  The  wheat  rust  can  be  used  for  the  practical  study.     If  the  cluster 
cup  on  barberry  cannot  be  had,  use  other  cluster  cups. 


280 


GENERAL   MORPHOLOGY   OF  PLANTS 


host,  give  a  rusty  appearance  to  them,  hence  the  name.  The 
mycelium  is  within  the  host  and  intercellular.  It  sends  short 
haustoria  into  the  cells,  where  they  absorb  nutriment.  In  many 
cases  it  causes  hypertrophy  of  the  host,  i.e.,  stimulates  the  affected 

part  of  the  host  to  ab- 
normal growth,  form- 
ing witches'  brooms  in 
one  form  on  the  bal- 
sam, or  galls  as  in  the 
case  of  the  cedar  apples 
(paragraph  456),  etc. 
Some  of  these  abnor- 
mal growths  are  edi- 
ble, as  the  branches 
of  an  acacia  in  India 
deformed  by  jEcidium 
esculentum.  and 


Fig.  244. 

Witches'  broom  on  balsam  (Abies  balsamifera)  caused 
by  a  parasitic  fungus  (^cidial  stage  of  Melampsorella 
cerastii),  from  northern  Michigan. 


in 

Scandinavia  the 
branches  of  the  fir  de- 
formed by  Mcidium 

corruscans.     The  life  history  is  very  complicated  in  some  species 

and  is  well  illustrated  by  the  wheat  rust. 

Wheat  Rust  (Puccinia  Graminis}. 

446.  The  wheat  rust  produces  one  of  the  common  rusts  on 
cereals  and  grasses  in  many  parts  of  the  world,  and  one  stage  in  its 
complete  life  history  occurs  on  the  barberry. 

447.  The  cluster-cup  stage  on  the  barberry. — The  diseased 
spots  on  the  leaves  of  the  barberry  are  yellowish  and  round. 
Upon  the  under  side  of  the  leaf  there  can  be  seen  minute  cup- 
shaped  structures  (aecidia)  distributed  over  the  spots.     These  are 
better  seen  with  the  aid  of  a  pocket  lens.     In  figures  248,  249,  a 
section  of  the  barberry  leaf  through  one  of  these  spots  shows  its 
relation  to  the  host  and  the  mycelium  between  the  cells.     The  cup 
is  formed  of  a  bundle  of  stout  hyphae  with  stout  short  cells  growing 
out  from  this  mycelium  and  bursting  through  the  epidermis  of  the 


FUNGI:    THE   RUST   FUNGI 


281 


leaf.  The  hyphae  of  the  outer  layer  are 
sterile,  and  remain  united  laterally  to  form 
the  wall  (peridium)  of  the  cup,  which  is  first 
closed  over  the  top  but  later  opens  out. 
The  cells  of  the  central  bundle  of  hyphae, 
in  chains,  separate  at  maturity  and  form 
the  cluster-cup  spores  (aecidiospores).  Upon 
the  upper  side  of  the  spot  are  much  smaller, 

yellow,  conical 
elevations,  seen 
in  cross  section 
at  fig.  249.  These 
are  the  spermo- 
gonia.  They 
produce  numer- 
ous very  tiny, 
rod  -  shape  d 
structures  which 
ooze  out  at  the 

flask-shaped 
spermogonia  in  a  gelat- 
inous mass,  sweetish  to 
the  taste.  Fertilization 
takes  place  by  the  fusion 
of  two  cells  in  adjacent 
rows  at  the  bottom  of  the 
young  cluster  cup  in  some 
cases,  and  by  the  migra- 
tion of  a  nucleus  from  a 
basal  cell  into  the  one 
above,  or  laterally  situ- 
ated in  other  cases.  The 
cluster-cup  spores  develop  in  chains  from  this,  each  having 
two  nuclei  which  do  not  fuse  until  the  final  stage  of  the  life  cycle 
is  reached  in  the  tehutospore  (paragraph  449). 


Figs.  245-247. 
Fig.  245. 

Barberry  leaf  with  two 
diseased  spots.  Natural 
size. 


Cluster-cup  stage  of  wheat  rust. 

Fig.  246.  Fig.  247. 

Single  spot,  show-  Two      cluster 

ing  cluster  cups  cups  more  en- 
larged, showing 
split  margin. 


enlarged. 


Fig.  248. 

Section  of  an  aecidium  (cluster  cup)  from  barberry 
leaf.     (After  Marshall-Ward.) 


282 


GENERAL   MORPHOLOGY   OF   PLANTS 


448.  The  red  rust  of  wheat  (uredo  stage).  —  The  aecidio- 
spores  from  the  cluster  cup  on  the  barberry  are  carried  by  the  wind 


Fig.  249. 


Section  through  leaf  of  barberry  at  point  affected  with  the  cluster-cup  stage  of    the  wheat 
rust;  spermogonia  above,  aecidia  below.     (After  Marshall-Ward.) 

to  the  wheat  (also  to  the  other  cereals  and  some  grasses).  Here 
they  germinate  and  the  mycelium  enters  at  a  stomate  and  pro- 
duces the  intercellular  mycelium.  At  certain  points  under  the 


Fig.  250. 

Fertilization  and  development  of  aecidiospores  in  a  rust,  Phragmidium  violaceum.  ep, 
epidermis  of  host.  st,  sterile  cells  at  ends  of  a-cidial  thread,  fc,  fertile  cells.  A,  part  of 
aecidial  stroma,  showing  two  binucleate,  fertile  cells.  B,  showing  nucleus  of  sperm  cell  at  base 
of  fertile  cell  passing  into  the  fertile  cell  at  the  side.  C,  similar  stage.  D-G,  different  stages 
in  formation  of  aecidiospores.  H,  mature  aecidiospore.  (After  Blackman.) 

epidermis  of  the  leaf,  or  stem,  a  group  of  short  spore-bearing 
hyphae  are  formed,  each  of  which  bears  a  broadly  elliptical  spore 
with  minute  warts  on  the  wall,  and  with  a  yellowish  oil  in  the  proto- 
plasm. These  spores  are  the  uredos ports.  The  pustule  formed 


i 


FUNGI:   THE  RUST  FUNGI 


283 


here  is  called  a  sorus.     The  epidermis  is  ruptured  by  the  growth 
pressure  of  the  hyphae  and  spores,  and  thus  the  spores  are  set 

n 


Fig.  251. 

Wheat  leaf  with  red 
rust.     Natural  size. 


Fig.  252.  Fig.  253.  Fig.  254. 

Portion      of      leaf        Natural  Enlarged, 

enlarged  to  show  sori.  size. 

Figs.  251-252.     Puccinia  graminis,  red-rust  stage  (uredo  stage). 
Figs.  253-255.     Black  rust  of  wheat,  showing  sori  of  teieutospores. 


Fig.  255. 
Single 
sorus. 


free.     These  uredospores  are  carried  by  the  wind  to  other  wrheat 
plants,  starting  new  centers  of  the  disease,  and  thus  several  suc- 


Fig.  256.  Fig.  257.                                   Fig.  258. 

Uredospores    of   wheat   rust,  Germinating  uredo-         Germ  tube  entering  the  leaf 

one   showing   remnant    of    the  spore  of  wheat  rust.  (After     through  a  stoma. 

pedicel.  Marshall-Ward.) 

cessive  crops  of  uredospores  are  formed  in  one  season.     The 
uredo  stage  is  the  propagative  stage. 


284 


GENERAL   MORPHOLOGY   OF  PLANTS 


449.  The  black  rust  of  wheat   (teleuto  stage). — On  the 

mycelium  which  originates  from  the  aecidiospores,  in  less  abun- 
dance on  that  which  originates  from  the  uredospores,  another 
kind  of  spore  is  formed,  the  teleutospore.  These  are  either  in 


B 

Fig.  259. 

A,  section  through  sorus  of    black  rust  of  wheat,  showing  teleutospores.      B,  mycelium 
bearing  both  teleutospores  and  uredospores.     (After  cle  Bary.) 

separate  sori  (a  teleutosorus)  or  they  are  mixed  in  with  the 
uredospores.  In  the  wheat  rust  the  teleutospores  are  two-celled, 
with  thick  brown  walls,  and  the  stalk  usually  remains  attached 
(ng.  259). 

450.  Germination  of  the  teleutospores  and  infection  of 
the  barberry. — The  teleutospores  of  the  wheat  rust  rest  during 
the  winter  on  leaves  and  stems  lying  on  the  ground.  In  the  spring 
each  cell  germinates,  putting  forth  a  tube  through  a  germ  pore 
near  the  apex  of  each  cell.  This  tube  is  the  promycelium,  which 
divides  quite  regularly  by  three  cross  walls  into  four  cells,  each  of 
which  forms  a  small  pointed  outgrowth,  the  sterigma.  Through 
this  the  protoplasm  in  the  cell  moves  out  and  forms  a  small  spore, 
the  sporidium.  This  sporidium  is  carried  by  the  wind  to  the 
barberry,  where  it  germinates,  the  tube  enters  between  epidermal 


FUNGI:    THE   RUST  FUNGI  285 

cells  into  the  barberry  leaf,  and  starts  the  cluster-cup  stage  again, 
thus  completing  the  life  cycle. 


Fig.  260.  Fig.  261.  •          Fig.  262. 

Teleutospore  germinating,         Promycelium  of  germinat-         Germinating  sporidia  enter- 
forming  promyceiium.  ing      teleutospore,     forming     ing   leaf  of   barberry   by   my- 

sporidia.  celium. 

Figs.  260-262.     Puccinia  graminis  (wheat  rust).     (After  Marshall- Ward.) 

451.  Races  of  the  wheat  rust. — There  are  some  peculiarities 
in  the  life  of  the  wheat  rust,  which  as  stated  above  occurs  on  oats, 
barley,  rye,  and  many  grasses.     For  example,  the  uredospores 
formed  on  the  oats  can  infect  oats  but  cannot  infect  wheat,  rye, 
barley,  and  some  grasses;  and  the  same  is  true  with  the  uredospores 
from  the  barley,  rye,  and  some  of  the  grasses,  —  they  cannot  infect 
the  oats  and  members  of  the  other  groups.     The  uredo-  and 
teleuto-spores  on  these  different  plants  cannot  be  distinguished  as 
to  form,   size,  etc.     They  constitute  physiological  races  which 
have  become  confined  to  certain  groups  of  hosts.     In  the  case  of 
all  of  these  races,  however,  the  sporidia  from  the  teleutospores 
can  produce  the  cluster  cups  on  the  barberry.     But  cluster  cups 
originating  from  oat  teleutospores  cannot  infect  wheat,  barley, 
rye,  etc.,  but  only  oats  and  the  members  of  the  oat  group. 

452.  How  the  wheat  rust  passes  the  winter  in  regions 
where  the  barberry  is  absent. — It  has  long  been  known  that  the 


286  GENERAL   MORPHOLOGY   OF   PLANTS 

wheat  rust  can  live  through  the  winter  in  the  teleutospore  stage. 
Since  the  sporidia  from  the  teleutospores  cannot  infect  the  cereals 
or  grasses  but  only  the  barberry,  the  appearance  of  the  wheat 
rust  in  early  spring,  in  regions  where  the  barberry  does  not  exist, 
has  long  been  a  mystery.  It  is  well  known  that  in  southern  lat- 
itudes, as  in  the  Gulf  States  in  America,  and  along  the  Mediter- 
ranean coast  in  Europe,  the  wheat  rust  can  live  through  the  win- 
ter in  grains  and  grasses  in  the  uredo  stage,  since  the  climate  is 
so  mild.  This  led  to  the  belief  that  southern  winds  in  the  spring 
bore  the  uredospores  northward  and  thus  produced  sudden  and 
widespread  infection  in  northern  latitudes.  This  probably  does 
occur  to  a  certain  extent.  But  recent  investigations  in  northern 
Europe,  in  Wisconsin  and  North  Dakota  show  that  the  uredo 
stage  of  some  of  the  grain  rusts,  formed  late  in  the  autumn,  lives 
through  the  winter  and  the  spores  germinate  in  the  spring.  The 
few  infections  from  these  early  in  the  spring  produce  centers  from 
which  a  second  widespread  and  serious  infection  follows.  In 
places  in  the  northern  peninsula  of  Michigan  the  ground  is  cov- 
ered so  deeply  with  snow  that  the  ground  does  not  freeze  in  the 
wheat  fields.  Fall  wheat  which  has  the  uredo  stage  on  it  can 
thus  carry  the  disease  over  the  winter.  The  mycoplasma  theory, 
propounded  by  the  Swedish  botanist  Eriksson,  according  to 
which  the  protoplasm  of  the  host  and  fungus  is  blended  during 
the  winter,  and  in  the  spring  the  fungus  plasma  can  withdraw 
from  this  mycoplasma  blend  and  form  the  mycelium,  is  not  gen- 
erally accepted. 

453.  Early  history  of  our  knowledge  of  the  wheat  rust. — 
This  history  makes  a  very  interesting  chapter  of  the  story  of 
botanical  investigations,  which  is  fascinating  to  read,  but  a  brief 
account  only  can  be  given  here.  A  half  a  century  ago  it  was 
supposed  that  the  four  forms  of  the  wheat  rust  described  above 
(^Ecidium,  spermogonium  or  ^cidiolum,  Uredo,  and  the  teleuto- 
stage,  or  Puccinia)  were  distinct  genera  of  plants,  and  that  the  two 
former  belonged  to  a  distinct  family  of  plants.  Prior  to  this  time, 
the  farmers  of  England,  in  the  early  part  of  the  i8th  century, 
believed  the  barberry  plant  caused  wheat  rust,  because  wheat 


FUNGI:    THE   RUST   FUNGI  287 

was  always  more  badly  rusted  on  the  leeward  side  of  barberry 
bushes.  As  early  as  1760  laws  were  passed  in  Massachusetts 
requiring  barberry  bushes  to  be  destroyed.  A  little  later  a 
Swedish  schoolmaster,  Schoeler  (in  1816),  carried  barberry  leaves 
with  the  cluster  cups  into  a  rye  field  and  rubbed  the  leaves  on  to 
the  rye,  so  that  he  could  see  the  masses  of  yellow  cluster-cup  spores 
on  the  rye  leaves.  These  rye  plants  became  badly  infected,  while 
the  remaining  plants  around  them  remained  healthy.  Finally, 
in  1864-5,  de  Bary,  a  celebrated  German  botanist,  demonstrated 


Fig.  263. 

Cedar  apples,  the  winter  condition.  Abnormal  growth  of  the  cedar  caused  by  a  fungus 
(Gymnosporangium  macropus).  The  masses  of  spores  ready  to  ooze  out  are  in  the  little  pits 
with  the  conical  elevations. 

by  experimental  studies  the  connection  of  the  cluster  cup  on  bar- 
berry with  the  uredo  and  teleutospores  on  wheat,  his  investiga- 
tions undoubtedly  being  stimulated  by  those  of  a  renowned  French 
botanist,  Tulasne,  who  had  previously  shown  the  connection  of  the 
uredo  and  teleuto  stages.  These  studies  have  since  been  verified, 
both  in  Europe  and  in  the  United  States,  in  regions  where  the 
barberry  grows. 

454.  Other  grain  rusts. — There  are  a  number  of  other  rusts 
which  attack  wheat  and  other  cereals.  One  of  the  most  destruc- 
tive of  these  in  this  country  is  Puccinia  rubigo-vera.  In  some 
regions  in  the  United  States  this  rust  is  more  abundant  and  does 
more  injury  to  the  wheat  than  the  Puccinia  graminis. 


288 


GENERAL    MORPHOLOGY   OF   PLANTS 


455.  Prevention  of  wheat  rust. — No  practical  method  has 
been  fouad  of  successfully  combatting  the  wheat  rust.  Formerly 
laws  were  enacted  in  England  and  Massachusetts  requiring  the 
destruction  of  the  barberry,  but  this  did  not  materially  lessen  the 
disease.  The  selection  of  resistant  varieties  gives  promise  of  solv- 
ing the  problem.  The  "  Marconi  "  wheats  are  more  resistant 
than  many  other  varieties,  and  experiments  in  crossing  are  being 


Fig.  264. 

Cedar  apples  after  the  spring  rains  begin.  The  mass  of  gelatin  swollen  by  the  rains 
is  oozing  out  in  strings  and  carrying  with  it  the  teleutospores  of  the  fungus  (Gymno- 
sporangium  macropus). 

made  with  the  hope  of  obtaining  still  more  resistant  strains  (see 
paragraph  663). 

456.  Cedar  apples  and  cedar  rust. — "  Cedar  apples  "  are 
galls  formed  on  the  leaves  and  young  twigs  of  the  cedar,  through 
the  stimulus  of  the  mycelium  of  one  of  the  rust  fungi.  These 
belong  to  the  genus  Gymnosporangium.  In  early  spring,  the 
teleutospores  formed  in  the  gall  the  previous  year,  in  little  nests, 
ooze  out  in  strings  in  wet  weather,  because  of  the  large  amount  of 


FUNGI:    THE   RUST  FUNGI 


289 


gelatinous  substance  formed  in  connection  with  the  teleutospores, 
which  absorbs  water  and  swells.  These  gelatinous  strings  of 
teleutospores  are  yellow  in  color.  The  teleutospores  germinate 
while  in  the  mass,  and  the  sporidia  are  carried  to  the  apple,  to  haw- 
thorns, and  other  trees  where  they  produce  the  cluster-cup  stage 
known  as  apple  rust,  etc.,  which  occurs  both  on  the  leaves  and 
fruit. 

457.  Life  history  of  the  wheat  rust. — The  complete  life 
history  of  the  wheat  rust  described  above  in  abbreviated  form  is 
as  follows,  remembering  that  the  mycelium  or  plant  is  present  in 
all  spore  forms  except  in  the  formation  of  the  sporidia  on  the 
promycelium. 


Fig.  265. 

^Ecidial    stage    (Roestelia)  of  Gymnosporangium,   showing   tube  of   the   cup   split   into 
numerous  slender  divisions  which  are  recurved  against  the  leaf.     On  leaves  of  Crataegus. 

^Ecidial  stage  with  spermogonia  on  the  barberry.  Jicidio- 
spores  carried  to  the  grasses  and  cereals.  Uredo  stage  with 
repeated  crops  of  uredospores,  the  uredo  stage  being  the  propa- 
gative  stage,  mycelium  finally  producing  teleutospores.  Teleuto- 
spores after  a  period  of  rest  *  produce  a  promycelium  from  each 
cell  with  four  sporidia.  The  sporidia  pass  to  the  barberry,  infect 
it,  produce  mycelium  which  gives  rise  to  more  spermogonia,  aecidia 
and  aecidiospores.  The  cycle  of  the  life  history  may  be  repre- 
sented by  the  diagram  III  A,  and  in  diagrams  B,  C,  D  are 


*  In  some  species  the  teleutospores  germinate  as  soon  as  they  are  mature, 
example,  the  hollyhock  rust. 


290 


GENERAL   MORPHOLOGY   OF  PLANTS 


shown  the  life  cycles  of  rusts  having  fewer  spore  forms.  For 
example,  some  lack  the  uredo  stage,  as  in  Puccinia  podophylli  on 
the  mandrake;  others  lack  the  aecidial  stage,  as  in. Puccinia  taraxaci 
on  the  dandelion;  while  still  others  lack  both  ascidia  and  uredo, 
having  only  the  spermogonia  and  teleuto  stage,  as  in  Puccinia 
malvacearum,  the  rust  of  the  hollyhock. 


Diagram  III.  Illustrating  life  cycle  in  the  development  of  the  four  different  form  cycles 
in  the  rusts.  The  heavy-walled  oval  bodies  enclosing  the  bold  face  No.  Ill  represent  the 
primary  teleutospore.  The  circles  with  the  bold  face  No.  I  represent  the  primary  aecidium. 
The  circles  with  the  short  radiations  or  spines  with  bold  face  No.  II  represent  the  primary 
uredo,  and  the  lighter  Nos.  1,  II,  III  in  the  figures  represent  the  corresponding  secondary 
ascidium,  uredo  and  teleutospore  stages  which  are  propagative,  and  thus  repeat  the  cycle. 
The  small  circle  connected  with  the  teleutospore  by  a  short,  narrow  line  represents  the 
promycelia  and  sporidia.  The  narrow  line  issuing  from  the  sporidium  represents  the  my- 
celium of  the  aecidial  stage,  the  cells  of  which  are  uninucleate.  The  small  elliptical  body 
connected  with  this  line  by  a  narrow,  short  line  represents  the  spermogonium;  the  cells  of 
this  are  also  uninucleate.  The  broad  lines  represent  the  mycelium  produced  by  the  germi- 
nation of  the  ascidio-  and  uredo-spores.  In  reading  the  cycle  pass  from  left  to  right. 

A  represents  the  cycle  of  those  species  having  all  four  spore  forms.  B  represents  the 
cycle  of  those  species  in  which  the  uredo  stage  is  absent.  C  represents  the  cycle  of  those 
species  in  which  the  secidium  is  absent.  D  represents  the  cycle  of  those  stages  in  which 
both  the  ascidium  and  uredo  are  absent. 


CHAPTER    XXIX. 
FUNGI    (Concluded). 

BASIDIUM   FUNGI   (Concluded). 
Mushrooms,  Bracket  Fungi,  Puf  balls,  etc. 

458.   The  mushrooms. — The  word  mushroom  was  formerly 
applied  to  certain  of  the  fleshy  gill-bearing  fungi,  and  probably  was 


Fig.  266. 
A  poisonous  "mushroom"  (Amanita  muscaria),  the  fly  agaric. 

first  used  for  the  common  cultivated  mushroom  (Agaricus  campes- 
tris},  which  also  grows  in  pastures,  lawns,  etc.  Some  use  the  word 
as  synonymous  with  all  the  basidium  fungi.  But  this  seems  too 

To  THE  TEACHER.  Either  the  common  mushroom  (which  usually  can  be 
obtained  in  the  market  during  the  winter)  or  one  of  the  other  agarics  should 
be  studied.  The  group  of  fungi  can  be  farther  illustrated  by  a  number  of  the 
bracket  fungi,  fairy  clubs,  puffballs,  earth  stars,  etc.,  which  are  easily  obtained 
and  preserved  dry.  It  would  be  an  excellent  plan  to  have  one  or  two  of  the 
poisonous  Amanitas  preserved  dry,  or  in  alcohol,  for  illustration. 

291 


2Q2 


GENERAL   MORPHOLOGY   OF   PLANTS 


broad.  Others  use  it  for  all  the  fleshy  larger  fungi,  including 
the  morel,  one  of  the  sac  fungi.  This  appears  to  be  a  better  use  of 
the  word.  The  word  toadstool  is  used  by  some  to  denote  the 
poisonous  species,  while  mushroom  is  applied  by  the  same  persons 
to  denote  the  edible  fungi.  But  few  of  the  advocates  of  this  dis- 
tinction between  mushroom  and  toadstool  know  what  constitutes 
a  toadstool,  and  call  many  edible  fungi,  toadstools.  Most  bot- 
anists make  no  distinction  between  the  words  but  use  them 
synonymously,  and  speak  of  edible  and  poisonous  mushrooms. 


Fig.  267. 
An  edible  "toadstool"  (Amanita  caesarea"),  Caesar's  agaric. 

These  higher  members  of  the  basidium  fungi  we  will  treat  under 
the  following  heads:  ist,  the  Gill  Fungi;  2nd,  the  Bracket  Fungi 
or  Pore  Fungi;  3rd,  the  Coral  Fungi,  or  Fairy  Club  Fungi;  4th, 
the  Hedgehog  Fungi,  or  Tooth  Fungi;  5th,  the  Puff  balls,  etc. 

The  Gill  Fungi. 

459.  The  gill  fungi. — The  gill  fungi  are  provided  with  thin 
narrow  leaf -like  outgrowths  on  the  underside  of  a  "  cap."  These 
gills,  or  lamellas,  stand  close  together  and  radiate  from  the  central 
part  of  the  under  surface  of  the  cap,  or  from  its  point  of  attach- 
ment with  a  stem,  or  wood  when  the  fungus  lacks  a  stem  and  the 


FUNGI:  GILL  FUNGI 


293 


Fig.  268. 
The  cultivated  mushroom  (Agaricus  campestris). 


cap  is  attached  directly  to  the  substratum.     These  thin  plates, 

or   lamella,   are   covered  with   the   club-shaped  structures,    or 

basidia,    which     are 

characteristic  of   the 

basidium     fungi. 

Where  these  basidia 

stand    side    by   side 

covering   extensive 

surfaces,    as    in   the 

higher     basidium 

fungi,    they    form    a 

fruiting     surface    or 

hymenium.    The  sur- 
face of  the  gills  then 

is  the  fruiting  surface 

of  the  gill  fungi.     Two  to  four  spores,  usually  four,  are  borne 

on  each  basidium. 

460.  The  common 
mushroom  (Agaricus 
campestris). — The 
parts  of  the  common 
mushroom  are  as  fol- 
lows. A  cylindrical 
stem,  or  stipe,  sup- 
porting a  circular  con- 
vex cap,  or  pileus. 
The  gills,  or  lamellae, 
are  attached  to  the 
underside  of  the  pileus 
and  are  closely 
crowded,  extending 
radially  from  near  the 
stem  to  the  margin 


g 


Fig.  269. 

Portion  of  section  of  lamella  of  Agaricus  campestris. 
tr.  trama;  sh,  subhymenium  ;  b,  basidium;  si,  sterigma 
(plural  sterigmata);  g,  basic! iospore. 


of  the  pileus,  the 
V-shaped  spaces  between  the  larger  ones  being  filled  in  by 
shorter  ones.  On  the  stem  is  a  thin  membranous  collar,  the 


294 


GENERAL   MORPHOLOGY   OF  PLANTS 


ring  or  annulus  (fig.  268).     In  fig.  269  is  a  section  of  the  gills 

showing  the  club-shaped  basidia  with    the    sterigmata  bearing 

the  spores.     In  the  cultivated  forms  there  are  often  only  two 

spores  to  a  basidium,  wh.le  in  the  field  form  there  are  usually 

four. 

461.   Development  of  the  mushroom.— The  development  of 

the  mushroom  is  briefly  as  follows:  The  mycelium  spreads  through 
the  soil  or  substratum,  forming  fine  white 
cords.  This  is  known  as  the  spawn. 
When  this  is  well  established  small  rounded 
compact  masses  of  mycelium  are  formed 
on  the  cords.  These  are  the  young 
fruit  bodies  which  are  to  develop  into  the 
mushroom.  When  they  become  from  3  mm. 
to  5  mm.  in  diameter,  the  parts  of  the 
mushroom  are  differentiated,  the  upper 
part  into  the  cap,  the  lower  part  into  the 
Portion  of  hymenium  of  stem,  and  the  outer  portion  midway  forms 
the  I'eil.  Inside  of  this  veil  the  hymenium 
begins  to  form  on  the  underside  of  the  cap, 

and  a  circular  opening  is  formed  by  the   parting  of  the  tissue 

between  the  veil,  the 

upper    part    of    the 

stem    and    the    cap. 

This  leaves  room  for 

the   development  of 

the  gills  which  grow 

downward   from  the 

cap.      This    is    the 

"button"    stage    of 

the   mushroom.     All 

parts    continue    to 

expand,    the     stem 

Fig.  271. 

elongates,       the      Cap        Cluster   of   young  mushrooms,  a  few  of   the  larger  ones 
,  developing  to  maturity. 

broadens,    and     the 

veil  becomes  well  formed.      Finally  the    veil    ceases   to    grow, 


FUNGI:   GILL   FUNGI 


295 


becomes  stretched,  breaks  away  from  the  margin  of  the  cap, 
and  is  left  as  a  collar  or  ring  on  the  stem.  .  The  gills  are 
first  pink,  then  become  dark  brown  or  blackish  as  the  spores 
with  brown  walls  ripen.  The  spores  then  fall  from  the  gills. 
Under  favorable  conditions  these  spores  germinate  and  produce 
more  mycelium  and  spawn. 
Besides  the  common  mush- 
room there  are  several  hun- 
dred edible  ones  in  many 
genera  but  they  cannot  be 
discussed  here. 

462.  Some  poisonous 
mushrooms.  —  The  most 
dangerous  poisonous  mush- 
rooms belong  to  the  genus 
A  manita.  The  genus  A  manita 
has  white  spores,  a  cap,  stem, 
and  ring  which  comes  from 
the  veil  as  in  the  common 
mushroom.  The  gills  are  free 
from  the  stem  or  lightly  at- 
tached and  the  stem  is  usu- 
ally easily  separable  from  the 
cap.  In  addition  there  is 
present  a  distinct  envelope, 
surrounding  the  entire  plant 
in  the  young  or  button  stage, 
known  as  the  volva,  which 
should  be  clearly  understood 
in  its  different  forms  in  order 
to  be  sure  of  the  genus.  Only  three  forms  of  the  volva  will 
be  described  here  in  the  following  species.  Amanita  phalloides, 
and  its  forms  or  closely  related  species,  is  the  most  dangerous 
one,  being  "  deadly "  poisonous.  The  species  in  its  typical 
form  in  Europe  has  a  greenish  or  greenish-brown  pileus.  The 
volva  splits  at  the  apex  as  the  plant  emerges  and  is  left  as  a 


Fig.  272. 

A  poisonous  mushroom  (Amanita  mappa), 
cap  pale  yellow  with  patches  of  a  delicate, 
floccose,  pale  brownish  substance;  veil,  stem 
and  gills  white;  under-surface  of  veil  sometimes 
very  pale  lemon  yellow;  upper  portion  of  bulb 
saucer  shaped.  X  i  diameter. 


296  GENERAL   MORPHOLOGY   OF   PLANTS 

prominent  sack  or  bag  around  the  base  of  the  stem.  Amanita 
verna  is  considered  by  some  as  a  white  form  of  this  species. 
This  is  common  in  America.  Amanita  map  pa  has  a  pale  yellow 
cap;  the  volva  splits  transversely,  leaving  portions  on  the  cap  in 
the  form  of  floccose  patches  or  warts.  The  lower  part  is  left  as 
a  narrow  rim  on  the  outer  edge  of  the  broad  bulb  of  the  stem. 
The  poisonous  principle  in  the  above  three  species  is  phallin,  a 
substance  thought  to  be  of  an  albuminous  nature.  It  dissolves 
the  blood  corpuscles  and  the  serum  escapes  into  the  alimentary 
canal.  No  antidote  is  known.  Another  poisonous  species  is 
Amanita  muscaria  (fig.  266),  the  "  fly  agaric."  It  has  a  red,  or 
yellowish  red  cap,  white  gills  and  stem.  The  volva  splits  trans- 
versely, the  upper  part  being  left  as  coarse  white  warts  on  the 
pileus  which  is  striate  on  the  margin.  The  lower  part  of  the  volva 
is  left  near  the  base  of  the  stem,  as  one  to  three  coarse  rings  on  the 
bulb.  The  poisonous  principle  in  the  fly  agaric  is  muscarine.  It 
paralyzes  the  nerves  which  control  the  action  of  the  heart,  and  if 
not  counteracted  results  in  death.  Hypodermic  injections  of  small 
doses  of  atropin  stimulate  the  heart  to  greater  activity,  thus 
counteracting  the  poison  until  its  effect  has  disappeared. 

Bracket  Fungi  or  Pore  Fungi. 

463.  The  bracket  fungi. — These  are  the  firm  fungus  growths 
of  a  shelving  form  so  common  on  dead  or  living  trees,  stumps, 
logs,  etc.,  in  the  forest.  The  under  surface  is  very  finely  honey- 
combed with  minute  tubes  or  pores  (characteristic  of  the  family 
Polyporacece).  The  fruiting  surface  or  hymenium  lines  all  these 
pores.  Some  of  these  bracket  fungi  are  hoof-shaped,  or  tongue- 
shaped.  They  grow  singly  or  in  clusters.  In  some  of  them  the 
age  can  be  determined  by  counting  the  number  of  concentric 
rings  on  top,  as  in  the  pine-inhabiting  polyporus  which  grows  on 
the  conifers,  the  charred  polyporus  growing  on  birch,  beech,  maple, 
oak,  apple,  etc.  One  of  these  has  been  found  which  was  eighty 
years  old.  This  one,  and  related  bracket  fungi,  were  used  in 
early  times  as  "  tinder  "  for  holding  and  lighting  fire.  Some  are 


FUNGI:   BRACKET  FUNGI 


297 


peeled  into  thin  strips  and  made  into  garments  by  peasants  of 
some   European  countries.     In  some   species   there   are   several 
rings  formed  each  year  on  the  surface  so  that  this  will  not  indi- 
cate   the    age,  as  in  the 
flattened  bracket  fungus, 
so  often  used  for  sketch- 
ing   or   writing    on    the 
under  surface.     But  the 
age  of  this  fungus  can  be 
determined  by  splitting  it 
in  two  along  the  middle, 
since  there  is  one  stratum 
of  tubes  formed  each  year 
on  the  underside.     Some 
of  the  bracket  fungi  are 
annual,   that  is,  they  die 
during  the   same   season 
in  which  they  are  formed, 
but  the  mycelium  may  live 
in  the    trunk  many  sea- 
sons, a  century  or  longer, 
every  now  and  then  pro- 
ducing  new    fruit    bodies.      Many  of   these   bracket  fungi  are 
called  wood-destroying  fungi,  because  the  action  of  the  mycelium 
is  so  destructive  to  timber  (see  paragraph  215).     Some  of  them 
are  called  "wound"  parasites,  since  they  can  only  enter  living 
trees  through  a  wound  in  the  cambium  layer,  or  when  a  limb  is 
broken  off,  or  carelessly  pruned.     The  heart  wood  being  dead 
the  mycelium  can  then  enter,  and  produce  heart  rot,  thus  destroy- 
ing the  timber  and  weakening  the  tree  and  its  roots.     Many  of  the 
pore  fungi  are  not  bracket  forms.     Some  are  spread  out  on  the 
surface  of  wood,  and  many  have  a  cap  and  central  stem.     The 
largest  number  of  those  with  central  stem  are  quite  large  fleshy 
fungi  belonging  to  the  genus  Boletus.     Some  of  these  are  edible 
as  the  "  Steinpilz  "  of  Germany,  or  the  "  cepes  "  of  France  (Bole- 
tus edulis}.     Some  are  said  to  be  poisonous.     Many  have  bright 


Fig.  273. 

Pine    inhabiting    Polyporus   (Polyporus   pinicola) 
growing  on  fallen  hemlock  log. 


298 


GENERAL   MORPHOLOGY   OF  PLANTS 


and  beautiful  colors.  The  flesh 
of  some  quickly  changes  to 
blue,  green,  or  red,  when 
bruised  or  cut. 

464.  The  coral  fungi,  or 
fairy  clubs  (Clavariaceae). — 
The  fairy  clubs  are  the  small, 
club-shaped,  fleshy,  basidium 
fungi,  growing  on  the  ground 
in  forests  and  groves.  The 
largest  one,  "  Hercules'  club" 
is  10-20  cm.  (4-8  inches)  long 
and  1-3  cm.  in  diameter.  The 
smallest  can  just  be  seen  with 
the  eye.  The  fruiting  surface 
covers  the  entire  surface  except 
the  lower  part  of  the  stem. 
They  grow  singly  or  in  clusters,  and  many  of  the  species  are 


Fig.  274. 

Charred  Polyporus  (Polyporus  igniarius) 
growing  from  knot  hole  on  beech.  X  i 
diameter. 


Fig.  275- 

Section  of  the  flattened  Polyporus  ( Polyporus  applanatus),  showing  two  layers  of  tubes, 
one  layer  developed  each  year. 

very  much   branched,  suggesting  a  coral-like  growth.     None  of 
these  are  known  to  be  poisonous. 


FUNGI:   BASIDIUM   FUNGI  299 

465.  The  hedgehog  fungi,  or  tooth  fungi  (Hydnacea). — The 
members  of  this  family  are  called  "  hedgehog  "  fungi,  or  "  tooth  " 
fungi  because  they  bristle  with  long  spines  which  hang  downward. 
Some  of  the  much  branched  forms  are  also  popularly  called  coral 
fungi.     The   fruiting   surface   covers  the  surface   of    the   spines 
which  are  often  called  teeth. 

466.  Puffballs,  earth  stars,  etc. — These  make  up  a  large 
group  of  fungi  containing  several  orders.     They  grow  on  the 
ground,  or  on  rotting  wood,  and  a  few  on  the  bark  of  living  trees. 


Fig.  276. 

Earth  stars  (Geaster  triplex),  showing  the  outer  layer  of  the  Avail  divided  in  a  star-shaped 
manner  and  recurved.  The  opening  where  the  spores  escape  is  in  the  conical  apex  of  the 
inner  layer. 

A  few  are  subterranean.  They  are  mostly  rounded  or  oval  in 
shape,  and  a  few  have  short  or  long  stems.  In  nearly  all,  the  fruit 
body  has  an  envelope,  the  wall  or  peridium,  which  opens  irregu- 
larly in  some,  as  in  the  giant  puffball,  or  with  a  minute  pore  at 
the  apex.  In  the  "  earth  stars  ''  the  outer  layer  of  the  wall  splits 
regularly  and  turns  back  in  the  form  of  a  star,  while  the  inner  layer 
opens  by  a  pore  at  the  apex.  The  interior  of  most  of  the  puffballs 
is  a  many  chambered  structure,  on  the  walls  of  which  the  fruiting 
surface  is  formed.  At  maturity  the  internal  tissue  mostly  breaks 
down  into  a  powdery  mass  which,  with  the  spores,  makes  the 
"  smoke  "  of  the  puffballs.  The  "  stink  horn  "  fungi  are  related 


3oo 


GENERAL    MORPHOLOGY   OF   PLANTS 


forms  in  which  the  fertile  interior  tissue  is  elevated  at  maturity 
by  an  expanding  structure  called  a  receptacle,  leaving  the  v/all  at 
the  base  in  the  form  of  a  sac-like  volva. 

COMPARATIVE    REVIEW    OF   THE    FUNGI.* 

467.  The   three   general   types   of   fructification. — While 
there  are  great  variations  in  the  special  methods  in  the  fruiting 

of  the  fungi,  i.e.,  in  the  pro- 
duction of  the  spores,  they 
can  all  be  assembled  into 
three  general  types  of  fruc- 
tification. In  each  of  these 
types  of  fructification  there 
are  structural  elements  in  the 
fruit  bodies  which  are  peculiar 
to  the  fungi  possessing  that 
method  of  fructification,  and 
which  bear  the  spores.  These 
are  as  follows:  ist,  the  spore 
case  (sporangium)  in  the  Class 
Phy  corny  cetes;  2nd,  the  sac 
(ascus)  in  the  Class  Ascomy- 
cetes;  and  3rd,  the  basidium 
in  the  Class  Basidiomycetes. 

468.  The  Class  Phy- 
comycetes. — The  members 
of  this  class  include  the  forms 
in  which  the  spore  case  is  the 
characteristic  fruit  structure. 
Together  they  make  up  the 
sporangium  series  or  spore 
case  series  of  the  fungi.  The  spore  case  contains  the  spores,  and 
is  for  the  most  part  what  is  called  a  generalized  structure,  because 
it  contains  often  a  large  and  usually  a  variable  number  of  spores 
even  in  the  same  species.  A  generalized  structure  is,  in  all  organ- 
*  For  reference. 


Fig.  277. 

"Stink  horn,"  or  "buzzard's  nose"  (Dic- 
tyophora  duplicata).      X  i  diameter. 


FUNGI:   BASIDIUM   FUNGI  30! 

isms,  regarded  as  indicating  a  low  type  of  organization  for  the 
plants  or  animals  possessing  it,  or  a  low  and  early  stage  in  the 
evolution  of  that  organ.  The  Phycomycetes  further  possess  a 
mycelium  in  which  there  are  few  or  no  cross  walls  dividing  it  into 
distinct  cells.  In  extensive  portions  of  the  mycelium  the  proto- 
plasm is  continuous  and  contains  many  nuclei.  The  mycelium  is 
ccenocylic,  or  the  plant  is  a  ccenocyte*  just  as  the  siphonaceous 
algae-like  Vaucheria  are  ccenocytes.  This  peculiarity  of  the 
mycelium  of  the  Phycomycetes,  together  with  the  method  of 
sexual  reproduction  by  antheridia  and  oogonia,  which  in  such 
forms  as  the  water  molds  greatly  resembles  that  of  such  algae  as 
Vaucheria,  has  led  many  to  believe  that  such  fungi  as  the  water 
molds  are  very  closely  related  to  such  algae  as  Vaucheria,  and  that 
the  water  molds  may  have  had  their  origin  from  the  siphon- 
algae,  by  some  of  these  algae  ages  ago,  becoming  parasitic,  or 
becoming  adapted  to  a  saprophytic  life,  as  a  result  of  which  they 
lost  their  chlorophyll.  From  this  point  of  view  there  is  a  two- 
fold reason  for  calling  the  Phycomycetes,  the  algal  fungi. 

469.  The  Class  Ascomycetes. — In  this  class  of  fungi  the  ascus, 
a  sac-like  structure,  containing  the  spores,  is  the  characteristic 
fruiting  structure.  The  number  of  spores  has  become,  in  most 

*  Coenocyte  means  a  colony  of  naked  cells,  or  a  colony  of  protoplasts 
which  are  not  separated  from  one  another  by  cell  walls,  each  protoplast  con- 
taining one  of  the  nuclei.  Such  a  plant  as  Vaucheria,  or  the  mycelium  of 
a  colony  of  a  fungus  like  the  bread  mold,  was  formerly  believed  to  represent 
a  single  cell,  since  the  definition  of  a  cell  at  that  time  predicated  a  cell  wall  for 
its  boundary.  This  theory  is  still  advocated  at  the  present  time  by  some. 
The  argument  in  favor  of  this  view  in  the  case  of  such  extensive  coenocytic 
thalli,  as  is  found  in  the  mucors  and  Vaucheria,  that  a  certain  amount  of 
cytoplasm  does  not  remain  permanently  associated  with  individual  nuclei, 
that  the  nuclei  move  about  in  the  cytoplasm  more  or  less,  does  not  appear 
to  be  very  convincing.  There  is  nothing  really  remarkable  in  this  exchange 
of  cytoplasm.  In  many  multicellular  plants  it  is  well  known  that  the  proto- 
plasts of  different  cells  are  connected  by  strands  of  protoplasm  through 
minute  perforations  in  the  intervening  cell  wall.  In  many  of  the  red  algae 
these  cytoplasmic  communications  are  often  of  considerable  size  and  there 
is  probably  cytoplasmic  interchange  between  the  different  protoplasts,  so 
that  the  nuclei  here  are  not  permanently  associated  with  the  same  cytoplasm. 


3O2  GENERAL    MORPHOLOGY   OF  PLANTS 

cases,  definite  in  number,  usually  eight,  but  in  some  cases  contain- 
ing multiples  of  eight,  and  in  others  containing  regularly  six,  or 
four,  or  two,  and  in  rare  cases  one,  while  there  are  a  few  in  which 
the  number  is  variable,  being  from  two  to  three  or  four  or  five. 
This  indicates  a  more  specialized  condition  than  in  the  Phycomy- 
cetes.  The  mycelium  is  regularly  septate.  All  of  these  charactjrs 
indicate  an  advance  over  the  Phycomycetes.  The  fruit  body  of 
the  Ascomycetes,  the  perithecium  or  asocarp,  recalls  the  cysto- 
carp  of  the  red  algae,  and  there  are  several  peculiarities  in  con- 
nection with  the  form  of  the  sexual  organs  and  in  fertilization  in 
some  of  the  sac  fungi,  which  resemble  those  of  the  red  algae. 
This  has  given  rise  to  the  theory  that  the  sac  fungi  have  had  their 
ancestors  among  the  red  algae  of  the  past,  and  that  they  have 
lost  chlorophyll  and  the  function  of  photosynthesis  by  becoming 
parasites,  or  in  an  adaptation  to  a  saprophytic  mods  of  life. 

470.  The  Class  Basidiomycetes. — The  basidium  is  the 
characteristic  fruit  structure  in  this  class  of  fungi.  It  is  a  single 
cell  of  a  specialized  form  in  the  higher  members  of  the  class. 
In  the  lower  forms  it  is  divided  into  four  cells  by  cross  divisions, 
or  perpendijular  divisions,  as  in  many  of  the  trembling  or  jelly 
fungi.  In  the  latter  there  is  one  spore  from  each  cell,  while  in 
the  former  there  are  usually  four  spores  from  the  single  cell, 
rarely  two  or  six.  In  the  smuts  the  number  of  cells  of  the 
promycclium  (which  is  basidium-like)  varies.  This  specialized 
structure,  with  the  definite  and  limited  number  of  spores,  also 
indicates  a  higher  stage  of  development  than  is  found  in  the 
Phycomycetes.  The  mycelium  is  septate,  often  there  are  buckle 
joints  at  the  cross  walls,  while  the  large  and  highly  specialized 
fruit  bodies  are  in  great  advance  over  the  Phycomycetes.  The 
fungi  of  this  class  also  are  believed  by  some  to  have  originated 
from  some  of  the  higher  algae  in  the  past.  The  cluster  cup  of 
the  rust  fungi  may  possibly  represent  the  cystocarp,  but  there 
is  little  else  to  suggest  an  ancestral  relationship,  unless  the  basidio- 
spores  represent  tetraspores,  and  in  the  rust  fungi  they  do  stand 
in  the  same  position  in  the  life  cycle  as  the  tetraspores  do  in  some 
of  the  red  algae. 


FUNGI  :   BASIDIUM  FUNGI  303 

471.  Two  theories  of  the  evolution  of  the  fungi. — There 
are  two  theories  of  the  evolution  of  the  fungi.  The  first  theory  is 
that  the  fungi  have  had  their  origin  at  different  points  from  the 
algae,  i.e.,  certain  groups  of  fungi  being  developed  off  from  cer- 
tain groups  of  algae  as  suggested  above.  The  second  theory  is 
that  the  fungi  represent  a  natural  group  of  plants,  and  that  this 
group  has  followed  a  line  of  development  of  its  own,  the  higher 
forms  being  developed  from  the  lower,  just  as  it  is  believed  that 
the  higher  algae  have  developed  from  the  lower.  There  are  a 
number  of  reasons  for  holding  this  theory.  One  of  the  foremost 
of  these  reasons  is,  that  there  are,  within  each  of  the  three  classes, 
such  manifest  evidences  of  lines  of  evolution  tending  to  show 
that  the  higher  forms  of  each  group  have  had  their  origin  among 
lower  members  of  the  same  group.  The  resemblances  to  the 
algae  may  be  accidental;  they  may  represent  cases  of  parallel 
evolution,  which  it  is  generally  believed  has  occurred  both  in 
certain  groups  of  plants  and  animals.  While  these  resemblances 
are  strong  in  some  points,  there  are  still  connected  with  them 
certain  structures  and  processes,  which  are  not  present  in  the 
algae.  We  probably  can  never  decide  which  theory  is  the  cor- 
rect one.  These  theories  may  continue  to  exist  side  by  side  as 
interesting  topics  for  speculation.  .  The  author  does  not  commit 
himself  wholly  to  either.  But  it  is  generally  accepted  that,  in 
the  study  and  classification  of  the  fungi  and  algae,  it  is  more  con- 
venient to  arrange  the  classification  according  to  the  second 
theory. 


CHAPTER   XXX. 
LIVERWORTS   (HEPATIC^). 

472.  General  characters. — The  name  liverwort  refers  to 
certain  plants  which  were  supposed  to  simulate  by  their  form  the 
organ  of  the  human  body  known  as  the  liver.  (The  hepatica,*  a 


Fig.  278. 
Thallus  of  liverworts  (Riccia). 

flower  of  the  woods  in  early  spring,  is  known  as  the  "  liver-leaf," 
or  noble  liverwort,  because  of  the  three-lobed  leaf.)     The  liver- 

To  THE  TEACHER.  If  the  length  of  the  course  will  not  permit  the 
practical  study  of  any  of  the  liverworts,  several  of  them  may  be  used  for 
illustration  for  the  student  to  observe  the  general  habit  and  character  after 
the  study  of  a  moss.  Where  there  is  time  for  the  study  Marchantia  may  be 
used,  and  some  of  the  foliose  liverworts  can  be  examined  to  note  the  differen- 
tiation of  a  thin  strap-shaped  thallus  or  body  into  one  with  stems  and 
leaves.  The  teacher  can  use  discretion  in  the  employment  of  other  ex- 
amples in  the  practical  work,  according  to  the  length  of  time  which  can  be 
devoted  to  the  study. 

*  Hepatica  triloba  =  Hepatica  hepatica. 

3°4 


LIVERWORTS 


305 


worts  make  up  a  class  of  low,  flowerless  plants  standing  above  the 
algae  and  fungi.  They  all  possess  chlorophyll.  In  many  of 
them  the  plant  body  is  flattened  and  leaf -like,  more  or  less  rounded 
in  some,  or  strap-shaped  in  others,  and  lobed  or  forked  in  various 
ways.  These  lobed  forms  suggested  the  name  liverwort  which 
has  been  adopted  as  the  name  of  the  class,  with  the  technical 
name,  Class  Hepatica.  This  plant  body  is  a  thallus,  a  word 
applied  to  those  low  plant  forms  which  are  not  divided  into  a 
true  stem,  leaf  and  root.*  They  are  attached  to  the  ground,  to 


Fig.  279. 

Section  of  thallus  of  Marchantia.  A,  through  the  middle  portion;  B,  through  the  marginal 
portion;  p,  colorless  layer;  chl,  chlorophyll  layer;  sp,  stomate;  h,  rhizoids;  b,  leaf-like  outgrowths 
on  under  side  (Goebel). 

tree  trunks,  or  rocks  by  slender  thread-like  outgrowths  called 
rhizoids,  through  which  much  of  the  water  and  mineral  foods  are 
absorbed.  Nearly  all  of  the  liverworts  grow  in  damp  situations, 
or  float  on  the  water.  The  male  and  female  organs  are  a  sperm 
case  (antheridium)  with  motile  sperms,  and  an  egg  case  (arche- 
gonium)  with  an  egg.  The  egg  case  of  the  liverworts  is  a  more 

*  The  word  thallophyte,  however,  technically  applies  only  to  the  algae 
and  fungi,  which  are  the  thallus  plants  par  excellence. 


306 


GENERAL    MORPHOLOGY   OF  PLANTS 


highly  developed  organ  than  the  egg  case  of  the  algae  and  fungi, 
as  will  be  seen  in  the  study  of  examples.  The  fruit  of  the  liver- 
worts is  a  capsule  containing  spores,  usually  borne  on  a  stalk. 


THALLOSE*    LIVERWORTS. 

473.  Marchantia. — The  thallose  liverworts  may  be  repre- 
sented by  a  study  of  Marchantia.  This  plant  grows  on  damp 
soil,  or  rocks  in  swampy  or  moist, 
shady  places.  The  thallus  is  rather 
broadly  strap-shaped,  notched  at  the 
end,  the  growing  point  residing  in  the 
notch.  There  is  a  "  midrib  "  extend- 
ing along  the  middle  line.  The  plant 
branches  in  a  forked 
manner,  but  often  only 
one  of  these  branches  con- 
tinues its  growth, 
thus  leaving  pro- 
jecting portions 
on  the  sides  of 
the  thallus.  Ex-  / 
amined  with  a 

,          ,       ,  ,  Fig.  280. 

nand      lens       tne  Male  plant  of  Marchantia  bearing  antheridiophores. 

upper  surface  is 

seen  to  be  marked  off  into  regular  rhomboidal  areas,  and  in  the 
center  of  each  is  a  stomate  opening  (fig.  279).  These  open  into 
quite  large  chambers  in  which  most  of  the  chlorophyll-bearing 
tissue  is  in  the  form  of  short,  upright  chains  of  cells.  This 
tissue,  with  the  epidermis,  belongs  to  the  upper  layer  of  the 
thallus.  The  lower  layer  lacks  chlorophyll,  containing  some 
cells  with  spiral  thickenings  and  bearing  the  rhizoids.  There 
are  numerous  slender  rhizoids  on  the  under  surface,  some  of 
which  have  numerous  thickenings  on  the  inside  of  the  wall. 
There  are  also  thin  membranous  scales  on  the  under  surface 

*  Those  liverworts  in  which  the  plant  body  is  a  true  thallus. 


LIVERWORTS 


307 


near   the   apex,  which  protect  the  growing   point.     The   plant 
is    diceceous    (or    heterothallic,    see    paragraph    407),    some    of 


Fig.  281. 
Marchantia  plant  with  cupules  and  gemmae;  rhizoids  below. 

them  being  male  and  others  female.  The  plant  propagates 
asexually  by  brood  buds  developed  in  little  cups  with  a  fringed 
edge,  formed  on  separate  plants  (fig.  281).  Each  of  these  buds  is 
a  miniature  thallus  of  Marchantia,  with  a  growing  point  in  a 
notch  at  two  opposite  points  in  the  flattened  nearly  circular  bud. 


II 


Fig.  282. 


Section  of   antheridial    receptacle  from   male  plant  of    Marchantia  polymorpha,  showing 
cavities  where  the  antheridia  are  borne. 


308 


GENERAL    MORPHOLOGY    OF   PLANTS 


474.  The  male  plants  and  sperm  cases  (antheridia). — The 
sperm  cases  are  borne  on  special  outgrowths,  the  gamete  bearer.* 
These  are  disk-shaped  and  stalked.  The  sperm  cases  are  in 
flask-shaped  cavities  of  the  upper  surface.  Each  sperm  case  is 

a  more  or  less  oval  body  like  a 
stalked  capsule  with  a  wall  of  a  single 
layer  of  cells.  The  interior  is  a  mass 
of  minute  cells  in  each  of  which  two 
sperms  are  formed.  Each  sperm  is  a 
long,  slender  body,  with  two  long,  very 
slender  cilia  which  lash  about  and 
cause  it  to  move  in  the  water. 

475.  The  female  plant  and  egg 
cases  (archegonia) . — The  egg  cases 
or  female  organs  are  also  borne  on 
special  outgrowths,  the  gamete  bearers. 
The  egg  gamete  bearer  is  shaped  some- 
thing like  the  sperm  gamete  bearer, 
-  2g3-  but  the  disk  is  divided  into  slender 

Section    of   antheridium  of  Mar- 
chantia,    showing     the     groups     of    rays     and 
sperm  mother  cells. 

the  stalk 

is  longer,  giving  it  an  umbrella 
shape  (fig.  285).  The  egg  cases 
are  borne  on  the  under  surface 
of  the  disk,  between  the  delicate, 
thin,  laminate  tissues  which  hang 
downward  and  protect  them  from 
drying  out.  Each  egg  case  is  a 
flask-shaped  structure  with  a  swol- 
len base  (venter),  and  a  long, 
slender  neck  with  a  canal  leading  F|!' 28,4'  . 

Sperms      of      Marchantia      uncoiling 

down   to    the   egg   in   the    basal  part,    and    one    extended,   showing    the    two 
30  ^         t  cilia. 

When  the    egg   is   ripe    the    canal 

opens,  and  if  a   sperm  enters  and  passes  into  the  egg,  it  unites 

with  the  egg  nucleus  and  fertilization  results. 


*  Gametophore,  because  it  bears  gametes. 


LIVERWORTS 


309 


476.  The  capsule  (sporogonium). — As  a  result  of  fertiliza- 
tion the  egg  does  not  develop  the  marchantia  plant  again,  but 
develops  into  a  new  structure  very  different  from  the  thallus 
which  bears  the  sexual  organs.  This  is  the  capsule  bearer 


Fig.  285. 
Marchantia  polymorpha,  female  plants  bearing  archegoniophores. 


(sporogonium},  which  is  peculiar  to  all  the  liverworts  and  mosses 
as  well.  In  Marchantia,  as  in  most  liverworts  and  mosses,  it  is 
a  stalked  capsule.  The  capsule  contains  the  spores,  and  in 
Marchantia  and  many  other  liverworts  the  spores  are  mixed 
with  sterile  cells  in  the  form  of  long,  slender,  spirally  marked  cells 
called  elaters.  These  elaters  are  very  sensitive  to  changes  in  the 
humidity  of  the  air,  twisting  and  coiling  in  various  ways  with 
slight  changes  in  the  humidity.  This  assists  in  pushing  the 
spores  out  of  the  capsule  after  it  opens  at  the  apex.  Since  the 


GENERAL   MORPHOLOGY   OF  PLANTS 


egg  cases   hang  downward  from  the  underside  of  the   gamete 
bearer,  the  capsule  also  grows  downward.    At  first  the  venter  of  the 


Fig.  286. 

Marchantia  pplymorpha,  archegonium  at  the  right  with  egg;  archegqnium  at  the  left  with 
young  spprogonium;  p,  curtain  which  hangs  down  around  the  archegonia;  e,  egg;  v,  venter  of 
archegonium;  «,  neck  of  archegonium;  sp,  young  sporogonium. 

egg  case  increases  in  size  to  form  a  hood  (calyptra)  which  protects 
the  young  egg  case.     The  hood  is  later  broken.     At  maturity  the 


Fig.  287. 

Section  of  archegonial  receptacle  of  Marchantia  po'.ymorpha;  ripe  sporogonia.  One  is  open, 
scattering  spores  and  elaters;  two  are  still  enclosed  in  the  wall  of  the  archegonium.  The  junction 
of  the  stalk  of  the  sporogonium  with  the  receptacle  is  the  point  of  attachment  of  the  sporophyte 
of  Marchantia  with  the  gametophyte. 

stalk   of   the    capsule   elongates   and    pushes    the    capsule    out 
from  between  the   delicate   tissue   membranes  which  protected 


LIVERWORTS 


the  egg  case  (fig.  287),  the  capsule  opens  and  the  spores  are 
scattered.  The  spores  germinate  under  favorable  conditions  and 
produce  the  thallus  of  the  marchantia,  thus  completing  the  life 
cycle. 

477.  Riccia. — Riccia   is   another   of    the  thallose    liverworts. 
The   plants   are  thin  and   leaf-like,  some  being  nearly  circular, 
others  semicircular,  others  narrowly  strap-shaped.     They  branch 
in    a    forked    manner    so    that    the 

circular  forms  are  split  or  indented 
inward  from  the  edge,  while  some 
of  the  strap-shaped  forms  produce 
rosettes.  They  grow  on  wet  ground 
or  float  on  the  water.  There  are  no 
special  outgrowths  on  which  the 
sexual  organs  are  borne.  The  sperm 
and  egg  cases  are  developed  in  the 
upp'er  side  of  the  thallus  along  the 
middle  line.  The  form  of  the  sexual 
organs  is  very  similar  to  those  of 
Marchantia.  The  capsule,  however, 
is  very  different.  It  is  a  simple  glo- 

,  j         i  i       Elater   and   spore    of    Marchantia. 

boSC  Capsule  Or  Spore  Case,  developed  spt  spore;  me,  mother  cell  of  spores, 
..  .  ,  .  ,  i  i  showing  partly  formed  spores. 

from    the  egg  within   the   enlarging 

venter  of  the  egg  case,  The  outer  layer  of  cells  is  sterile,  while 
the  inner  portion  forms  nothing  but  spores,  four  spores  being 
formed  from  a  single  mother  cell  as  in  Marchantia.  All  of  the 
mother  cells  in  Riccia  form  spores,  while  in  Marchantia  some  of 
them  form  sterile  cells,  the  elaters.  Marchantia  and  Riccia  each 
represent  a  group  of  the  thallose  liverworts  including  many  other 
closely  related  forms. 

478.  The  foliose  liverworts. — These  are  the  leafy-stemmed 
liverworts.     Each  plant  is  really  a  thallus,  but  is  highly  special-- 
ized  by  the  formation  of  a  distinct  slender  axis  (the  stem)  and 
thin  foliar  organs  (the  leaves).     This  has  probably  come  about 
by  a  lobing  of  the  margins  of  thallose  forms,  which  became  more 
and  more  marked  and  specialized  until  these  leafy-stemmed  forms 


Fig.  288. 


312 


GENERAL   MORPHOLOGY   OF   PLANTS 


were  developed.     The  prominent  leaves  are  in  two  lateral  rows, 

but  there  is  an  inconspicuous  third  row  on  the  underside.     The 

stems  are   creeping  or   ascending.     They   are   attached  to   the 

soil,  to  logs,  or  tree  trunks,  by 

rhizoids.     They  are  sometimes 

mistaken   for   mosses.*    Many 

of  the   foliose   liverworts  grow 

in  moist  situations,  as  on  the 

trunks  of  trees  in  the  forest  or 

in  groves,  where  in  dry  weather 


nt 


Fig.  289.  Fig.  290. 

Section    of     developing     sporogonia    of  Foliose     liverwort,    male    plant    showing 

Marchantia;    nt,  nutritive  tissue  of   game-         antheridia  in  axils  of  the  leaves  (a  junger- 
tophyte;   st,  sterile  tissue  of  sporophyte;  sp,         mannia). 
fertile    part    of    sporophyte;    va,    enlarged 
venter  of  archegonium. 

they  would  be  in  danger  of  being  killed  were  it  not  for  some 
special  peculiarity  in  their  form,  etc.  One  of  these  (Frullania) 
has  oval  leaves  closely  crowded  and  overlapping  each  other  on 
*  Most  mosses  are,  however,  more  or  less  erect;  the  leaves  are  in  three 
distinct  rows  and  equal  in  size,  except  in  certain  forms.  Vegetative  stems 
of  Mniunt,  one  of  the  mosses,  are  creeping,  and  there  are  two  prominent 
lateral  rows  resembling  a  liverwort.  So  in  Fissidens,  another  moss,  the 
prominent  leaves  are  in  two  lateral  rows  and  the  stems  are  more  or  less 
inclined  or  creeping  as  in  some  liverworts.  The  leaves  of  liverworts  always 
consist  of  a  single  layer  of  cells,  while  in  the  mosses  there  is  a  midrib  of 
more  than  one  cell  in  thickness  extending  part  way  into  the  base  of  the  leaf, 
or  entirely  through  the  leaf,  except  in  the  peat  mosses. 


HORNED    LIVERWORTS  313 

the  stem.  The  plant  clings  very  closely  to  the  bark  of  the 
tree  which  aids  in  retaining  moisture.  In  addition  each  of  these 
leaves  has  a  lobe  on  the  under  side  (next  the  tree) 
which  is  sac -like  and  holds  water.  This  water  is  doled 
out  to  the  plant  during  dry  periods.  It  remains  so 
long  in  these  pockets  that  minute  animals  belonging 
to  the  crustacean  group  make  it  their  home.  In  Cali- 
fornia one  of  the  liverworts  growing  on  the  ground 
forms  subterranean  tubers  which  tide  the  plant  over 
the  dry  season. 

479.  The  capsule   (sporogonium)  of  the  leafy- 
stemmed  liverwort. — This  is  a  stalked  capsule,  and 
the  capsule  splits  down  to  the  base  into  four  valves. 
In  some  species  elaters  are  mixed  with  the  spores. 

Fig.  291. 
HORNED  LIVERWORTS    (ANTHOCEROTES).         piaFnJuiciinf 

foliose    liver- 

480.  The  horned  liverworts. — The  horned  liver-  J£JJ-  ^^[y 
worts  may  be  represented  by  Anthoceros.     It  grows  in  fj™fjfpj5jjh 
wet,  muddy  places.     The  thallus  is  thin,»dark  green,  g^'piam6 
and  irregularly  branched  and  overlapping  (fig.  292). 

The  sexual  organs  are  immersed  in  the  thallus,  the  sperm  cases 
in  groups  in  a  cavity,  while  the  wall  of  the  immersed  egg  case 
is  united  with  adjacent  cells  of  the  thallus.  The  capsule  is 
long,  slender  and  slightly  curved,  its  form  suggesting  the 
name  of  "  horned  "  liverworts.  Its  base  is  surrounded  by  a 
slender,  short  outgrowth  of  the  thallus.  The  growing  point 
of  the  capsule  is  near  the  base,  the  older  portions  being  con- 
stantly raised  by  growth  at  the  base.  The  capsule  consists  of 
a  wall  and  a  column  of  sterile  tissue,  between  which  is  a 
layer  of  spore-bearing  tissue  in  the  form  of  a  tube.  Some  of 
the  cells  of  this  spore-bearing  tissue  are  mother  cells  of  spores, 
each  mother  cell  forming  four  spores.  Other  cells  alternating 
with  them  form  short,  spirally  marked  elaters.  From  the 
nature  of  its  growth  the  spores  at  the  apex  are  older  than 
those  below.  The  capsule  at  maturity  splits  longitudinally  and  the 


314 


GENERAL   MORPHOLOGY   OF  PLANTS 


spores  escape.     The  wall  cells  of  the  capsule  contain  chlorophyll, 
and  stomates  are  present  in  the  surface  layer.      It  is  thus  able  to 

make  its  own  carbohydrate 
food,  but  is  dependent  on  the 
thallus  for  its  water  and  min- 
eral food.  It  is  thus  more 
highly  developed  and  special- 
ized than  in  the  other  liver- 
worts. For  this  reason  the 
horned  liverworts  are  by  some 
placed  in  a  separate  class,  An- 
thocerotes. 

481.  Comparative  review 
of  the  liverworts.  —  The 
thallus,  or  plant  body,  of  the 
liverworts  on  which  the  sex- 
ual organs  are  borne  pre- 
sents two  forms.  First,  the 
thallose  forms  in  which  the 
plant  body  is  simply  a  green, 
leaf-like  or  strap-shaped 
structure  of  very  different 
form  in  different  genera. 
Second,  the  foliose  forms 
in  which  the  thallus  is  more 
specialized,  being  differen- 
tiated into  a  slender  axis  with  thin,  leaf-like  expansions.  The 
liverworts  are  nearly  all  land  forms,  adapted  to  growing  on  soil 
and  rocks  in  wet  or  moist  situations,  or  on  logs  or  tree  trunks, 
some  of  the  latter  being  adapted  to  resist  dessication  in  dry  sea- 
sons. The  sperm  case  does  not  show  much  advance  over  that  of 
some  of  the  higher  algae,  but  it  is  a  more  massive  structure,  and 
the  sperms  are  quite  different  and  more  highly  specialized  in 
form.  The  egg  case  shows  a  great  advance  in  structure  com- 
pared with  the  egg  case  of  the  algae,  being  a  multicellular  organ, 
flask-shaped  in  form.  The  greatest  advance  over  the  algae  is 


Fig.  292. 

Anthocercs  gracili=.  A,  several  gametophytes, 
on  which  sporangia  have  developed;  B,  an  enlarged 
sporogonium,  showing  its  elongated  character  and 
dehiscence  by  two  valves,  leaving  exposed  the 
slender  columella  on  the  surface  of  which  are  the 
spores;  C,  D,  £,  F,  elaters  of  various  forms; 
G,  spores.  (After  Schiffner.) 


LIVERWORTS  31$ 

shown  in  the  capsule  (sporogonium).  This  is  a  specialized 
structure  developed  from  the  egg,  which  is  very  different  in  form 
from  the  thallus,  and  its  function  is  the  development  of  spores 
which  produce  new  thallus  plants  and  serve  to  propagate  the 
liverworts  (a  few  are  propagated  also  asexually  by  brood  buds  as 
in  Marchantia}.  Among  the  liverworts  the  capsule  shows  con- 
siderable progress  in  development,  from  the  simple  spherical 
body  in  Riccia,  with  a  single  layer  of  wall  cells  surrounding  the 
spore-bearing  tissue,  and  the  short-stalked  capsule  in  Marchantia, 
to  that  of  the  foliose  liverworts,  where  the  capsule  is  long-stalked 
and  is  more  highly  specialized,  splitting  at  maturity  into  four 
valves  (except  in  a  few  forms).  But  the  highest  specialization  is 
reached  in  Anthoceros  where  the  capsule  has  a  definite  growing 
area,  the  wall  is  provided  with  stomates  and  chlorophyll,  and 
the  amount  of  spore-bearing  tissue  is  very  much  less  in  propor- 
tion to  the  sterile  portion.  These  characters  of  the  capsule 
are  of  greater  importance  in  showing  relationship  among  the 
liverworts  than  the  form  of  the  thallus.  The  marchantia  and 
riccia  forms  are  all  thallus  plants  with  a  comparatively  simple 
capsule.  They  belong  to  the  Order  Marclwntiales.  The  foliose 
liverworts  have  a  more  highly  specialized  capsule  (the  capsule 
four-valved).  They  belong  to  the  Order  Jungermanniales,  but 
some  members  of  this  order  also  are  thallose  liverworts.  The 
highest  liverworts  are  represented  by  Anthoceros  with  its  highly 
specialized  capsule.  They  belong  to  the  Order  Anthocerotales ; 
They  are  also  thallose  liverworts. 

482.  Alternation  of  generations. — It  is  now  time  to  note 
an  important  biological  principle  in  the  life  history  and  devel- 
opment of  plants,  viz.,  what  is  usually  called  "  alternation  of 
generations  "  The  thallus  with  its  sexual  organs  is  the  first  gen- 
eration, while  the  capsule  is  the  second  generation.  The  cap- 
sule is  developed  from  the  fertilized  egg  on  the  thallus,  and  the 
thallus  is  developed  from  the  spore  borne  in  the  capsule.  There 
is  thus  an  alternation  of  the  thallus  and  capsule,  or  an  alternation 
of  these  generations.  This  does  not  mean  that  this  alternation  is 
strictly  carried  out.  The  thallus  is  usually  perennial  and  lives 
for  many  years,  developing  capsules  perhaps  each  year. 


CHAPTER   XXXI. 
MOSSES    (MUSCINE^E). 

483.  General  characters. — The  mosses  are  small,  leafy- 
stemmed  plants  usually  growing  in  dense  tufts  or  mats  on  the 
ground,  in  swamps,  moist  woods,  or  in  dry  places,  on  rocks, 
or  on  tree  trunks,  etc.  Some  of  those  on  rocks  and  in  dry 
places  can  resist  long  periods  of  drought,  becoming  very  dry, 
and  revive  with  the  advent  of  rains.  A  few  grow  in  the  water. 
Those  not  found  in  the  water  are  nearly  all  erect,  with  three 
distinct  rows  of  leaves,  and  they  are  thus  easily  distinguished 
from  the  foliose  liverworts  (see  paragraph  478).  The  leaves 
consist  of  a  single  layer  of  cells,  except  for  a  more  or  less 
well  developed  midrib,  which  in  some  species  only  extends 
a  short  way  in  the  base  of  the  leaf;  in  other  species  it  is 
longer  and  in  some  extends  entirely  through  the  leaf.  This 
midrib  consists  of  narrow  cells  several  layers  in  thickness. 
Since  the  leaf  is  mostly  one  cell  layer  in  thickness,  the 
starch  grains  in  connection  with  the  chlorophyll  body  are 
easily  seen  with  the  aid  of  the  microscope.  The  spores  from 
the  capsule  germinate  and  produce  a  branched  filamentous 
growth,  the  protonema,  from  which  the  leafy  stem  arises  as  a 
branch.  The  general  characters  should  be  studied  in  one  or 
more  examples  followed  by  a  study  of  the  life  history.  The 
"fruit"  of  the  moss  is  a  stalked  capsule  (sporogonium) ;  rarely 
is  it  sessile.  The  stalk  is  inserted  in  the  end  of  the  moss  stem 

To  THE  TEACHER.  One  moss  (Mnium,  Polytrichum  or  Funaria)  should 
be  studied  in  practical  work.  A  very  interesting  collection  of  mosses  can 
easily  be  made  and  preserved  dry  on  cards  to  illustrate  the  different  habits 
of  the  mosses.  In  field  trips  made  during  the  year  members  of  the  class 
will  find  it  interesting  to  assist  the  teacher  in  making  such  a  permanent 
collection  for  the  school. 

316 


MOSSES  317 

or  in  the  end  of  a  short  branch  in  some  species.  The  sexual 
organs  are  sperm  and  egg  cases  (antheridia  and  archegonia). 
They  are  borne  usually  in  different  groups  on  the  end  of  the 
stem  or  a  short  branch,  either  on  the  same  plant  (moncecious,  or 
homothallic)  or  on  different  plants  (dioecious,  or  heterothallic). 


Fig.  293. 
Pigeon  wheat  mass  (Polytrichum)  in  fruit. 

484.  The  hairy-cap  moss  (Polytrichum). — The  hairy-cap 
moss,  or  as  it  is  sometimes  called  the  "  pigeon  wheat "  moss,  is 
an  excellent  one  for  study  because  of  its  common  occurrence 
and  wide  distribution,  its  large  size,  and  the  striking  difference 
between  the  male  and  female  plants.  It  grows  usually  in  mod- 
erately moist  situations  or  in  swampy  ground.  The  plants  form 
dense  tufts  or  an  extensive  turf,  the  male  and  female  plants 
usually  grouped  by  themselves.  The  leaves  are  quite  narrowly 
pointed  and  rather  rigid.  The  male  plants  are  shorter  than  the 
female  plants,  and  at  the  end  of  the  stem  the  leaves  are  crowded 
into  a  spreading  rosette,  in  the  center  of  which  the  sperm  cases 
are  crowded.  In  the  female  plants  the  terminal  leaves  are  rather 


GENERAL   MORPHOLOGY   OF  PLANTS 


appressed  into  a  tuft  so  that  they  protect  the  egg  cases  and  young 
fruit  body.  At  the  base  of  the  stem  are  numerous  thread-like 
rhizoids  usually  brownish  in  color.  In  the  moss  Mnium,  the 
male  plants  are  also  shorter  than  the  female  ones,  and  the  leaves 
at  the  apex  of  the  stem  form  a  rosette.  There  are 
also  prostrate  stems  with  two  rows  of  lateral  prom- 
inent leaves,  the  third  row  on  the  underside 
being  rudimentary.* 

485.  The  sexual  organs. — The 
sperm  cases  (antheridia)  are  crowded 
at  the  apex  of  the  male  shoot,  and 
intermingled  with  peculiar  club- 
shaped  bodies  (paraphyses)  which 
contain  chlorophyll.  The  sperm  case 
is  more  broadly  clavate,  and  consists 
of  a  wall  of  a  single  layer  of  cells 
containing  the  sperm  cells.  When 
the  sperms  are  mature  the  sperm 


Fig.  294. 
Female  plant 
(gametophyte)  of 
a  moss  (Mnium), 
showing  rhizoids 
below,  and  the 
tuft  of  leaves 
above  which  pro- 
tect the  arche- 
gonia. 


Fig.  295. 
Male      plant 

(gametophyte)  of  case  is  ruptured  at  the  apex  by  the 

a  moss  (.vlnium), 

showing  rhizoids  pressure   resulting  from  the  absorp- 

below    and     the    r 

antheridia  at  the  tion  of  water,  and  the  mass  of  sperm 

center  above  sur- 
rounded by  the   cells  escapes.     The  sperms  uncoil  and 

rosette  of  leaves. 

swim  about  until  some  finally  reach 
the  egg  case.  They  are  long  and  slender  with  two  long  cilia  at 
the  smaller  end.  The  egg  cases  (archegonia)  are  borne  in 
groups  on  the  end  of  the  female  shoot.  An  egg  case  is  flask- 
shaped,  with  a  short  stalk  which  lifts  the  base  a  little  distance 
from  the  end  of  the  shoot.  The  base  is  called  the  venter, 
and  the  slender  portion  the  neck.  A  canal  is  formed  in  the 
neck  at  maturity  by  the  dissolving  of  the  central  row  of  cells, 
which  leads  into  the  venter.  In  the  venter  is  the  egg. 

486.  The  moss  fruit  (sporogonium) . — The  moss  fruit  con- 
sists of  a  capsule  supported  on  a  slender  stalk.  In  the  hairy-cap 
moss  this  capsule  is  a  short,  four-angled  structure,  at  first  covered 


*  Such  a  stem  is  dorsiventral,  and  resembles  the  stems  of  the  foliose  liverworts 
which  are  also  dorsiventral.  In  the  moss  Fissidens  all  the  stems  are  dorsiventral. 


MOSSES 


319 


by  a  hairy,  conical  cap  "or  hood  (the  calyptra).  When  the  hood 
is  removed  the  appearance  of  numbers  of  these  capsules  on  their 
slender  stalks  perhaps  suggested  the  name  of  "  pigeon  wheat." 


Fig.  296.  Fig.  297. 

Section  through  end  of  stem  of  female  plant  Antheridium  of 
of  Mnium,  showing  archegonia  at  the  center.  Mnium  with  jointed 
One  archegonium  shows  the  egg.  On  the  paraphysis  at  the 
sides  are  sections  of  the  protecting  leaves.  left;  sperms  at  the 

right. 


At  the  apex  of  the  capsule  is  a  minute  "  lid  "  (the  operculum) 
which  is  easily  removed,  exposing  the  "  mouth  "  of  the  capsule 
(the  stomium).  Around  the  edges  of  the  mouth  are  numerous 
minute  pointed  processes,  the  teeth,  64  in  one  circle  or  row. 
There  is  another  inner  row  of  thinner  teeth. 

487.  Many  mosses  have  a  double  row  of  teeth,  others  have 
but  a  single  row,  while  some  have  no  teeth.  In  one  little  moss 
common  on-  decaying  logs  in  woods  there  are  only  four  teeth 
(Tetraphis  pellucida  =  Georgia).  Some  have  16,  others  32,  etc. 
The  teeth  are  usually  very  sensitive  to  changes  in  the  humidity 
of  the  air,  spreading  apart  in  moist  weather,  thus  permitting  the 
spores  to  escape,  or  closing  in  dry  weather.  The  spores  are 
formed  in  a  special  spore-bearing  tissue,  which  is*  in  the  'form  of  a 
hollow  tube  in  the  middle  part  of  the  capsule.  The  tube  is  filled 


320 


GENERAL   MORPHOLOGY   OF  PLANTS 


with  sterile  tissue,  and  also  surrounded  by  sterile  tissue.     These 
tissues  together  form  an  elliptical  body  which  is  suspended  in 


Fig.  298. 


Fig.  299. 


Funaria  hygrometrica.     A  ,  a  young  leafy  stem^-,       The  mouth  of  the  capsule  K  of  Fonti- 
with   the  calyptra  c.     B,  a    plant  g  with  the  al-   nalis  antipyretica.     Outer  peristome  ap, 
most  mature  sporogpnium,  of  which  s  is  the  seta,  inner  peristome  z/>.     (After  Sachs.) 
f  the  capsular  portion,*:  the  calyptra.     C,  longi- 
tudinal section  of  the  capsular  portion  dividing  it 
into   two   symmetrical   halves;    d  the   lid,  a   the 
annulus,  /  the  peristome,  c,  d  the  columella,  h 
air-space,  s  archesporium.     (After  Sachs.) 


an  air  chamber  within  the  capsule  by  delicate  threads  (fig.  298). 
The  spore-bearing  tissue  consists  of  a  single  layer  of  mother  cells, 
each  one  of  which  forms  four  spores. 

488.  Life  history  of  the  mosses. — The  life  history  of  the 
mosses  is  as  follows.  The  spores  germinate  and  produce  a  much- 
branched  filamentous  growth,  the  protonema,  which  means  first 
thread.  This  protonema  resembles  superficially  some  of  the 
filamentous  green  algae,  but  the  cross  walls  are  often  oblique  and 
this  serves  at  once  to  distinguish  them.  The  protonema  forms  a 
thin  or  rather  dense  web  on  the  ground  or  on  rotten  wood.  The 
leafy-stemmed  moss  plant  arises  from  this  as  a  stouter  branch, 
with  the  oblique  walls  regular  and  close  together.  Rhizoids  are 
developed  from  the  base  of  the  leafy  stem  and  sometimes  quite 


MOSSES 


321 


high  up  on  the  stem.  Numerous  leafy  stems  arise  from  the 
protonema,  thus  making  dense  tufts.  The  protonema  usually 
disappears  soon  after  the  moss  stems  arise.*  Certain  species  of 
the  mosses  often  multiply  by  branching,  by  the  growth  of  new 


Fig.  300. 

Funaria  hygrometrica.  A ,  germinating  spore;  v,  vacuole;  w,  rhizoid;  s,  exosporium.  B, 
portion  of  a  developed  protonema,  about  three  weeks  after  germination;  A,  a  prostrate 
primary  shoot  with  brown  wall  and  obliquely  transverse  septa,  from  which  proceed  the 
ascending  branches  with  limited  growth;  at  K  the  rudiment  of  a  leafy  axis  with  rhizoid  w. 
(After  Sachs.) 

protonemes  from  the  moss  plant,  and  sometimes  by  bulbils  f  or 
by  brood  buds.  After  the  development  of  the  sexual  organs, 
fertilization  is  brought  about  by  the  sperm  passing  down  the 
canal  of  the  egg  case,  and  fusing  with  the  nucleus  of  the  egg. 
The  fertilized  egg  then  divides  and  elongates  downward  to  form 
a  foot,  which  wedges  its  way  into  the  upper  end  of  the  moss  stem, 
while  the  upper  part  elongates  upward  to  form  the  stalk  and 
capsule.  At  the  same  time  the  egg  case  enlarges  to  form  a  pro- 

*  In  one  genus,  Pogonatum,  the  protonema  exists  for  a  long  time,  even 
until  the  fruit  of  the  moss  appears.  Here  the  protonema  is  more  con- 
spicuous than  the  moss  plant  and  covers  extensive  patches  of  the  ground 
along  the  roadside  in  woods.  The  protonema  in  a  few  of  the  higher  mosses 
is  partly  thallose,  as  in  Tetraphis. 

f  In  the  mosses  these  "  bulbils  "  are  small,  rounded  masses  of  cells. 


322  GENERAL   MORPHOLOGY   OF   PLANTS 

tective  covering  for  the  capsule  while  it  is  young.  Finally  the 
egg  case  is  torn  away  at  its  base  and  is  raised  aloft  on  the  capsule 
to  form  the  hood  or  cap  (the  calyptra).  With  the  ripening  of  the 
spores  in  the  capsule,  the  life  history  is  complete,  and  the  capsule 
opens  by  the  lid  to  permit  their  escape.  In  some  of  the  lower 
mosses  there  is  no  lid  on  the  capsule,  and  it  opens  irregularly. 

489.  The  peat  mosses. — The  peat  mosses  belong  to  a  dis- 
tinct order  (Sphagnales)  of  the  mosses.  They  are. called  peat 
mosses  because  the  accumulation  of  the  dead  parts  for  centuries 
forms  one  kind  of  peat.  They  grow  in  moors  (or  bogs)  where 
there  is  an  abundance  of  water,  or  in  very  damp  places  in  woods, 
or  even  on  the  faces  of  rocks  where  water  is  constantly  trickling 
down.  The  protonema  is  thallose,  and  the  leafy  stem  arises  from 
this  as  a  branch.  They  continue  to  grow  and  branch  year  after 
year,  the  stems  dying  away  below.  Because  of  the  great  quan- 
tity of  water  in  their  tissues  and  in  the  ground,  decay  is  slow 
and  only  partial,  because  the  water  largely  excludes  the  air 
which  is  necessary  for  the  activity  of  the  bacteria  and  fungi  which 
cause  the  decay  of  vegetation.  Their  partially  decayed  remains 
then  form  the  peat.  The  quantity  of  water  held  by  the  peat 
mosses  can  be  seen  by  squeezing  a  handful,  when  an  abundance 
of  water  is  wrung  out.  The  peculiar  character  of  the  peat  mosses 
which  enables  them  to  hold  water  is  as  follows :  There  are  numer- 
ous lateral  feathery-like  branches  which  stand  out  straight  from 
the  main  stem.  These  are  the  primary  branches.  Secondary 
branches  arise  from  these  close  to  the  main  stem  and  hang 
downward  around  it.  In  the  leaves  there  are  dead  cells  alter- 
nating with  the  green  living  ones.  These  dead  cells  have  lost 
their  protoplasm,  have  numerous  perforations  in  their  walls  and 
also  thickenings.  As  the  plants  stand  close  together  in  dense 
tufts  or  swards,  and  the  leaves  are  crowded  together  especially  on 
the  pendent  branches,  capillarity  draws  water  up  from  below 
and  it  is  stored  in  these  empty  dead  cells.'  With  the  partial 
decay  of  the  vegetation  in  these  peat  moors  there  is  an  abun- 
dance of  humic  acid  which  also  assists  in  preserving  the  material 
from  further  decay.  Peat  is  sometimes  pressed  into  firm  blocks 


MOSSES 


323 


and  used  for  fuel.  Peat,  especially  fern  peat,  is  often  used  by 
florists  for  mixing  in  soil  for  growing  certain  plants.  The  peat 
mosses  are  collected  and  used  for  packing  plants  and  other 
objects  for  shipment. 

490.  Fruit  of  the  peat  mosses. — The  fruit  of  the  peat  mosses 
is  a  capsule  with  a  broad  foot  inserted  in  a  naked  stalk  which  is 
an  outgrowth  of  the  leafy  stem.  The  naked  stalk  of  the  peat 
mosses,  then,  is  not  a  part  of  the  capsule.  The  capsule  is  not 
so  complicated  a  structure  as  that  of  the  higher  mosses  (Bryales). 


Fig.  301. 
Peat  mass  (Sphagnum)  in  fruit. 

491.  Importance  of  mosses  in  nature. — The  peat  mosses, 
assisted  by  other  plants  which  grow  in  similar  situations,  build 
up  ground  in  low  marshy  places.  They  assist  in  filling  in  small 
or  large  ponds,  beginning  on  the  shore.  This  they  are  enabled 
to  do  because  of  the  formation  of  the  peat;  the  plant  parts  in  the 
water,  not  being  able  to  decay,  build  up  ground  quite  rapidly. 
The  mosses  of  all  kinds  on  the  forest  floor  hold  considerable 


324  GENERAL   MORPHOLOGY   OF  PLANTS 

amounts  of  water,  and  thus  assist  the  leaves  and  humus  in  hold- 
ing back  the  water  after  rains,  so  that  it  does  not  run  off  so  rapidly, 
thus  lessening  the  danger  of  floods.  On  rocks  they  behave 
much  as  the  lichens  do  in  holding  decaying  vegetation,  and 
adding  to  the  humus  from  their  own  remains.  They  are  thus 
important  as  early  soil  builders. 

492.  Alternation  of  generations. — The  alternation  of  gen- 
erations in  the  mosses  is  similar  to  that  in  the  liverworts.  The 
protonema,  and  the  leafy-stemmed  moss  plant  with  the  sexual 
organs,  make  the  first  generation,  while  the  capsule  (with  its 
stalk)  is  the  second  generation.  In  a  continuance  of  the  com- 
plete life  cycle  there  is  an  alternation  of  these  two  generations. 
The  first  generation  is  independent  of  the  second  when  once 
started,  and  can  live  from  year  to  year,  often  multiplying  Vege- 
tatively  and  spreading  by  branching,  by  new  protonema,  and  by 
bulbils.  The  capsule,  however,  is  dependent  on  the  first  gener- 
ation, since  it  has  no  roots  or  rootlets  by  which  it  becomes  free 
and  established  as  an  independent  plant.  This  is  an  important 
biological  principle  in  the  life  history  and  development  of  plants. 
Very  few  of  the  algae  show  it.  The  fertilized  egg  usually  at  once 
develops  the  first  generation  again.  In  Coleochaete  there  is  a  second 
generation.  In  some  of  the  red  algae  (as  in  Polysiphonia,  Rhab- 
donia,  etc.)  the  tetraspore  plant  represents  a  second  generation.  It 
is,  however,  independent,  and  of  the  same  form  as  the  sexual  plant 
and  grows  under  the  same  conditions.  In  plants  showing  an  alter- 
nation of  generations  between  a  sexual  stage  and  an  asexual  stage 
developed  from  the  fertilized  egg,  the  first  generation  is  often 
spoken  of  as  the  gamete  plant  (gametophyte),  because  it  bears  the 
gametes  or  sexual  organs.  The  second  generation  is  likewise  called 
the  spore  plant  (sporophyte),  because  it  bears  the  spores.  The 
capsule  (and  stalk  when  present)  of  the  liver  worts  and  mosses 
is,  therefore,  the  spore  plant  stage  (sporophyte)  of  these  plants, 
while  the  thallus  with  the  sexual  organs,  the  leafy-stemmed  plant 
of  the  foliose  liverworts,  the  protonema  and  leafy-stemmed  moss 
plant,  is  the  gamete  plant  stage  (gametophyte).  Each  one  of 
these  stages  begins  and  ends  with  a  single  cell.  The  gamete 


MOSSES  325 

plant  begins  with  the  spore  and  ends  with  the  unfertilized  egg 
in  the  egg  case.  The  spore  plant  begins  with  the  fertilized  egg 
and  ends  with  the  mother  cell  (of  the  spores)  in  the  capsule. 


Diagram  No.  IV.  Illustrating  the  life  cycle  of  the  Bryophytes  (a  liverwort  or  moss). 
Course  of  development  follows  the  direction  indicated  by  arrows.  The  zygote  is  the  fertil- 
ized egg.  Vegetative  multiplication  by  buds  and  filamentous  outgrowths  of  the  thallus. 
Note  increase  of  sporophyte. 

493.  Comparative  review  of  the  mosses. — The  first  genera- 
tion (or  gametophyte)  of  the  mosses  begins  with  the  spore  which 
produces  the  protonema,  either  a  branched  filamentous  green 
growth,  or  a  thallose  one  as  in  the  peat  mosses.     This  suggests 
that  the   ancestors  of   the   mosses  were   plants  resembling  the 
algae  or  liverworts,  though  no  alga  or  liverwort  is  now   known 
which  could  be  regarded  as  an  ancestor  of  the  mosses.     From 
the  protonema  the  leafy-stemmed  moss  plant  is  developed  as  a 
branch.     This  bears  the  sexual  organs.     The  second  generation 
(or  sporophyte)  is  developed  from  the  fertilized  egg.     It  remains 
dependent  on  the  leafy  stemmed  plant  for  its  food,  the  stalk  being 
wedged  into  the  tissues  of  the  stem.     The  capsule  of  the  mosses 
is  a  much  more  highly  developed  and  complex  structure   than 
that  of  the  liverworts,  and  shows  that  the  mosses  stand  higher  in 
the  scale  of  classification  and  development  than  the  liverworts. 

494.  Relationship  of  the  liverworts  and  mosses. — There 
are,  however,  taken  as  a  whole,  very  close  relationships  between 
the  liverworts  and  mosses,  shown  in  the  character  of  the  sexual 
organs,   and  especially  in  the  capsule,  though  there  are  great 


326  GENERAL   MORPHOLOGY   OF   PLANTS 

differences  between  such  a  simple  one  as  is  found  in  Rictia, 
where  the  egg  develops  into  a  rounded  mass  of  spores  surrounded 
by  a  single  layer  of  sterile  cells,  and  the  very  complicated  capsule 
(spore  plant  stage)  of  the  higher  mosses  supported  on  a  stalk. 
The  intermediate  forms  show  intermediate  steps  in  this  speciali- 
zation. The  spore  plant  (or  sporophyte)  in  all  agrees,  however, 
in  being  dependent  on  the  gamete  plant  for  its  nourishment,  in 
not  possessing  leaf-like  outgrowths,  and  in  the  formation  of  a 
capsule  for  the  production  of  the  spores.  For  these  reasons  the 
liverworts  and  mosses  together  make  up  one  of  the  great  branches 
of  the  plant  kingdom,  called  the  Bryophytes,  or  moss-like  plants. 

495.  *  Formula  for  the  life  history  of  liverworts  and 
mosses. — The  asexual  stage  in  the  liverworts  and  mosses  is  the 
capsule  (with  the  stalk  when  present)  or  spore  plant  (sporophyte), 
and  alternating  with  the  first  generation,  the  gamete  plant 
(gametophyte).  The  formula  may  be  represented  thus 


/  anthendia  —  sperm  gamete  x         ...     , 

Gametophyte  C       ,  /  Fertilized   egg  — • 

N  archegoma  —  egg  gamete     / 

Sporophyte  —  asexual  spores  —  Gametophyte,  etc.,  which  reduced 

hfmmpc 


G  — <S>—  FE  — S  — asp  — G.,  etc. 


*  For  reference. 


CHAPTER   XXXII. 


FERNS    (CLASS   FILICINE^E). 


496.   General   characters.— 

The  ferns,  because  of  the  attrac- 
tive foliage  of  many  species,  are 
often  grown  for  ornament,  and 
this  has  led  to  their  being  most 
generally  known,  though  com- 
paratively few  persons  know  their 
structure  and  the  course  of  their 
life  history.  The  fern  plant  has 
a  true  stem,  roots  and  leaves, 
and  in  this  respect  is  very  dif- 
ferent from  the  moss  plant,  where 
the  stem  and  leaves  have  resulted 
from  the  differentiation  of  a  thal- 
lus.  The  leaves  (often  called 
fronds)  possess  chlorophyll,  and 
perform  the  function  of  photo- 
synthesis, while  the  roots  are  in 


Fig.  302. 

Walking  fern  (Camptosorus  rhizophyllus). 
Young  ferns  developing  from  the  slender 
tips  of  the  leaves. 


To  THE  TEACHER.  One  of  the  ferns  should  be  studied  carefully  in  the 
practical  work.  Prothallia  can  often  be  found  growing  spontaneously  on  the 
soil  of  pots  in  greenhouses  where  ferns  are  kept.  If  not  they  can.be  grown 
from  the  spores.  Often  one  can  interest  a  gardener  in  the  greenhouse  to 
assist  in  growing  them  or  they  can  be  grown  in  the  laboratory.  A  per- 
manent collection  of  a  number  of  the  local  ferns,  which  the  students  could 
assist  in  making,  can  be  used  to  illustrate  variations  in  habit,  dimorphism, 
etc.  Where  greenhouses  or  conservatories  are  near  the  students  can  visit 
them  to  inspect  tropical  ferns  as  well  as  other  interesting  plants.  If  the  time 
allotted  to  the  course  is  too  short  for  practical  study  of  the  higher  fern  plants 
dried  examples  of  the  horse  tail,  club  mosses,  etc.,  can  be  used  for  illus- 
tration. 

327 


328  GENERAL   MORPHOLOGY   OF  PLANTS 

the  soil  and  supply  the  water,  and  mineral  and  nitrogenous 
foods.  The  fern  plant,  then,  lives  independently  of  any  thal- 
lus.  The  stems  are  very  short  and  erect  as  in  the  Christmas 
fern,  or  are  creeping  or  underground  rhizomes  as  in  the  poly- 
pody, the  sensitive  fern,  or  the  common  brake,  while  in  some 
tropical  ferns  there  are  tall,  massive  trunks  as  in  the  tree  ferns. 
The  leaves  have  a  simple  blade  as  in  the  "  heart's  tongue  " 
(Scolopendrium  v ulgare  =  Phyllilis  scolopendrium},  or  are  once 
pinnate  as  in  the  polypody  and  Christ- 
mas fern,  or  twice  pinnate  as  in  many 
others,  while  in  the  common  brake 
they  are  palmately  branched,  the  main 
branches  being  twice  pinnate.  The 

leaves   of    ferns    are 

more      conspicuous 

than  the  stems,  and 

the  leaf  stalk  is  often 

mistaken  for  a  stem 

by  some.     The  ferns 

have   no  flowers  nor 

seeds.     They    are 

propagated  chiefly  by 

spores,  though  a  few 
Fig.  303.  develop  bulbils.*    In  Fjg 

"Fruit"    dots   of  the    {he    "  walking  "    fern  "Fruit"  dots  of  the  maidenhair 

common  polypody  fern.  fern. 

the  long,  slender  tips 

of  the  leaves  touch  the  ground,  take  root  and  develop  a  new 
stem  and  leaves,  thus  acting  like  a  stolon.  The  spores  are 
developed  in  spore  cases  (sporangia)  usually  clustered  on  the 
underside  of  the  leaves  in  groups  or  lines.  The  fern  plant  is 
the  second  generation  (spore  plant  or  sporophyte).  The  first 
generation  (gamete  plant  or  gametophyte),  which  is  developed 

*  Cystopteris  bulbifera  ( =  Filix  bulbifera]  which  grows  along  moist,  shady 
banks,  and  Asplenium  bulbiferum  which  is  often  grown  in  greenhouses.  In 
the  former  species  these  bulbils  fall  to  the  ground  and  grow  to  new  fern 
plants,  The  bulbil  of  the  fern  is  a  bud  developed  on  the  leaf. 


FERNS  329 

from  the  spores,  is  thallose,  and  called  a  prothallus  or  prothallium. 
It  is  quite  small,  thin  and  heart-shaped  in  many  species,  and 
bears  the  sexual  organs  on  the  underside.  There  are  also  rhi- 
zoids  which  attach  it  to  the  substratum  and  supply  water  and 
mineral  foods,  while  chlorophyll  in  the  prothallium  enables  it  to 
make  its  own  carbohydrate  food.  It  is  thus  able  to  lead  an 
independent  existence.  The  character  of  ferns  can  be  observed 
by  the  study  of  a  few  examples. 

SOME    OF    THE    COMMON    FERNS. 

497.  The  polypody  fern  (Polypodium  vulgare). — This  is 
one  of  the  common  ferns.  It  grows  in  the  open  woods,  often 
near  cliffs,  on  the  ground  or  on  rocks.  The  stem  is  creeping  (a 


Fig.  305.  Fig.  306. 

Christmas  fern  (Aspidium  Rhizome  of  sensitive  fern  (Onoclea  sensibilis). 

acrostichoides). 

root-stock).  On  the  ground  the  stem  often  lies  just  beneath  the 
leaves,  while  on  the  rocks  it  is  usually  exposed.  Near  the  grow- 
ing end  it  is  covered  with  numerous  brown  scales.  The  roots 
are  numerous,  finely  fibrous  and  black.  The  leaves  are  very 
conspicuous  and  arise  in  a  cluster  from  the  apex  of  the  stem. 
They  are  once  pinnate,  the  blade  being  divided  to  the  midrib 
on  either  side  into  numerous  linear  divisions.  Some  of  the 
leaves  are  sterile  while  others  are  fertile.  In  the  fertile  ones 
the  spore  cases  are  collected  into  roundish  groups  (sori,  a  single 
one  a  sorus),  these  groups  forming  two  rows,  one  on  either  side  of 
the  mid-vein  of  each  pinna. 


330  GENERAL   MORPHOLOGY    OF   PLANTS 

498.  The    Christmas    fern    (Aspidium    acrostichoides  = 
Polystichum  acrostichoides). — This  is  one  of  the  shield  ferns. 
It  grows  in  shady  woods.     The  stem  is  very  short  and  upright. 
The  leaves  are  pinnate,  and  are  of  two  kinds,  sterile  and  fertile. 
The  outer  ones  are  often  sterile,  while  the  inner  ones  in  a  cluster 
are  often  fertile.     These  are  easily  distinguished  from  the  sterile 
ones,  because   the  pinnae  which  bear  the  spore  cases  are  very 
much  shorter  and  are  narrower  than  the  sterile  ones,  even  on  the 
fertile  leaves.     It  is  only  the  upper  third,  or  half,  of  the  leaf, 
which  bears  fertile  pinnae.     The  sori  form  two  crowded  rows  on 
the  underside  of  each  pinna.     Each  sorus  is  covered  by  a  shield- 
shaped  structure  called  an  indusium,  which  protects  the  spore 
cases  when  they  are  young,  but  dries  and  withers  as  they  ripen, 
so  that  the  spore  cases  dry  out,  open,  and  scatter  their  spores. 

499.  The  bracken  fern  or  brake  (Pteris  aquilina  =  Pteri- 
^ium  aquilinum). — This  is  one  of  the  large,  coarse  ferns  which 
grow  in  open  sunny  places,  sometimes  covering  large  areas  and 
becoming  a  nuisance  as  a  weed.     The  stem  is  a  hard,  black, 
somewhat  woody  structure,  and  grows  as  a  root-stock  several 
centimeters   (8-12   cm.  =  3-5   inches)    under   the  surface  of    the 
ground.     The  leaves  are  the  only  portion  of  the  plant  seen  above 
the  ground.     They  have  long,  stout,  shining,   blackish  stalks  or 
petioles.     The  leaf  is  first  divided  in  a  palmate  manner  into 
three    stout    branches    (ternately    divided)    and    each    of    these 
branches   is  bipinnate,   the   final   pinnae    forming   narrow,    thin 
lobes.     The  spore  cases  (sporangia)  form  a  long  sorus  near  the 
margins  of  the  underside  of  the  pinnae,  and  the  margin  is  incurved 
over  them  for  protection. 

500.  Structure  of  the  spore  cases  (or  sporangia)  of  ferns. 
— In  most  of  our  common  ferns  (in  the  family  Polypodiacex]  the 
structure  of  the  spore  case  is  as  follows.     There  is  a  slender  stalk 
consisting  of  about  three  rows  of  cells.     This  supports  the  spore 
case.     This  is  a  rounded,   somewhat  compressed  or  biconvex 
structure,  with  a  wall  of  a  single  layer  of  cells.     As  seen  from  a 
side  view  there  is  a  row  of  specialized  cells  which  extends  from 
the  stalk  upward  and  over  the  top  about  three-fourths  the  dis- 


OF   THE 

UNIVERSITY 

Of 


FERNS 


tance  around.  This  row  of  cells  is  known 
The  inner  walls  of  the  cells  are  thick  and  firm.  The  perpen- 
dicular walls  are  thick  next  the  inner  wall  and  taper  outward, 
but  are  quite  rigid.  The  outer  and  lateral  walls  are  thin  and 
membranous,  this  ring  standing  out  quite  prominently  above  the 
lateral  faces  of  the  spore  case.  On  the  opposite  edge  of  the 
spore  case  from  the  ring  are  two  cells  near  the  middle  of  the  edge 
which  fit  together  somewhat  like  lips.  They  are  called  "  lip  " 
cells,  and  the  point  between 
them  is  the  "  mouth  "  (or 
stomium),  for  when  the  spore 


Fig-  307-  Fig.  308. 

Rear,  side,  and  front  view?  of  fern  spor-  Dispersion    of    spores  from  sporangium  of 

angium.   d,  c,  annulus;  a,  lip  cells.  Aspidium     acrostichoides,    showing     different 

stages  in  the  opening  and   snapping  of    the 
annulus. 

case  opens,  it  opens  between  these  two  cells.  In  the  interior  of 
the  spore  case  are  usually  sixteen  spore  mother  cells  in  this 
family.  Each  of  these  forms  four  spores,  so  that  there  are 
sixty-four  spores  in  a  spore  case. 

501.  Opening  of  the  spore  case  and  scattering  of  the 
spores. — When  the  spores  are  ripe,  the  indusium,  or  other  cover- 
ing of  the  sorus,  dries  and  withers,  exposing  the  spore  case. 
These  then  begin  to  dry.  In  doing  so  the  water  evaporates  from 
the  cells  of  the  ring.  The  air  cannot  enter  these  cells,  conse- 
quently there  is  great  air  pressure  from  the  outside  as  the  water 
slowly  escapes.  The  inner  walls  of  the  ring  cells,  as  well  as  the 
perpendicular  walls  between  its  cells,  are  firm  and  do  not  bend 
inward.  But  the  outer  and  lateral  walls  being  thin  and  mem- 


332 


GENERAL   MORPHOLOGY   OF  PLANTS 


branous  are  pressed  inward.  This  exerts  a  pull  on  the  outer 
edges  of  all  of  the  perpendicular  cell  walls,  which  act  as  so  many 
fulcra,  and  the  outer  edges  of  these  different  walls  are  brought 
nearer  and  nearer  together.  This  causes  the  inner  walls  to 
curve  slowly  outward  in  unison.  The  result  is  that  the  entire 
ring  begins  to  straighten  out.  The  lower  end  is  held  firmly  at 
the  base  of  the  spore  case.  The  lip  cells  are  torn  apart,  the 
upper  one  being  raised  by  the  straightening  ring.  At  the  same 
time,  the  two  lateral  faces  of  the  spore  case  are  torn  across,  and 
as  the  ring  curves  backward  it  carries  with  it  the  upper  half  of 
the  spore  case  and  nearly  all  the  spores.  When  the  ring  has 
curved  back  so  that  it  is  almost  doubled  on  itself,  it  suddenly 
snaps  back  again  nearly  to  its  former  position,  and  scatters  the 
spores  (fig.  308). 

502.    Structure  of  the  fern  stem. — The  stems  of  ferns  are 
provided   with    a   well-developed    fibro-vascular    system    which 


Fig.  309. 

Concentric  bundle  from  stem  of  Polypodium 
vulgare.  Xylem  in  the  center,  surrounded  by 
phloem,  and  this  by  the  endodermis.  (From 
the  author's  Biology  of  Ferns.) 


par. 


62 


Fig.  310. 

Section  of  stem  (rhizome)  of  Pteris 
aquilina.  sc,  thick-walled  scleren- 
chyma;  a,  thin-walled  sclerenchyma; 
par,  parenchyma. 


serves  for  transport  of  water  and  also  strengthens  the  stems. 
The  bundles  are,  however,  usually  concentric  instead  of  collateral  as 
in  the  higher  plants  (see  paragraphs  94,  98).  The  wood  is  in  the 
center  and  is  surrounded  by  the  bast,  the  bast  by  the  bast  sheath, 
and  this  by  the  endodermis,  thus  giving  a  concentric  arrange- 
ment (fig.  309).  While  the  bundles  strengthen  the  stems,  they 
are  comparatively  weak,  and  in  many  fern  stems  there  are  large 


FERNS 


333 


areas  of  stony  tissue  (sclerenchyma)  which  give  the  chief  mechan- 
ical support  (fig.  310). 

503.  Structure  of  the  fern  leaf. — In  many  respects  the 
leaves  of  ferns  are  similar  in  structure  to  the  leaves  of  the  flower- 
ing plants  (paragraphs  140-145).  The  blade  of  the  leaves  is 
thin  and  expanded,  and 
shows  the  same  light  rela- 
tion as  the  leaves  of  the 
higher  plants.  There  is  a 
layer  of  epidermal  cells  on 
either  side  of  the  leaf, 
which  are  quite  regular  as 
seen  in  cross  section  of 
the  leaf,  but  meet  by  very 
irregular  edges  in  surface 
view.  There  are  numerous 
stomates  which  are  pro- 
tected by  two  crescent- 
shaped  guard  cells  as  in 
the  higher  plants.  The 
mesophyll  of  the  leaves 
consists  usually  of  a  pali- 
sade layer  next  the  upper 
epidermis,  while  the  rest 
is  made  up  of  the  loose 
parenchyma  or  spongy  tis- 
sue with  large  intercellular 
spaces  which  communicate 
with  the  stomates.  The 
disk-shaped  chlorophyll 
bodies  lie  in  the  cells  of  the  loose  parenchyma,  the  palisade  and 
guard  cells,  and  sometimes  in  cells  of  the  epidermis.  In  the 
veins  are  the  vascular  bundles.  In  the  arrangement  of  these 
veins  is  shown  one  of  the  differences  in  structure  from  that  of 
the  higher  plants.  The  veins  branch  in  a  forked  manner,  which 
sometimes  is  very  striking.  The  vascular  system  strengthens 


Fig.  311. 

Rhizome  with  bases  of  leaves,  and  roots  of  the 
Christmas  fern. 


334 


GENERAL    MORPHOLOGY   OF   PLANTS 


the  leaves  and  leaf  stalks,  and  provides  for  transport  of  water 
and  food  solutions.  The  development  of  the  leaf  also  differs,  in 
that  the  basal  portion  develops  first  and  the  apical  portions  are 
successively  developed.  The  leaf  is  circinate  in  its  development. 
The  leaf  is  coiled,  and  as  it  develops  it  gradually  uncoils.  This 
is  very  striking  in  some  of  the  large  ferns  grown  in  greenhouses, 
but  is  also  easily  observed  in  our  ordinary  ferns. 

LIFE    HISTORY    OF    FERNS. 

504.  The    prothallium    and    sexual    organs. — The    spores 
from  the  spore  cases  germinate  and  produce  the  prothallium, 


Fig.  312. 

Spore  of  Pteris  serrulata, 
showing  the  three-rayed 
elevation  along  the  side  of 
which  the  spore  wall  cracks 
during  germination. 

which  is  the  first  gene- 
ration or  gamete  plant. 
At  first  a  short  thread  of 
two  to  three  cells,  con- 
taining chlorophyll,  is 
developed  from  the 
spore.  This  is  called  the 
protonemal  thread.  A 
rhizoid  is  developed  from  the  first  cell  of  this  thread.  The  ter- 
minal cell  divides  in  two  directions,  forming  a  flattened  green 
body,  the  young  prothallium.  Later  it  becomes  more  or  less  heart- 
shaped  in  outline,  one  cell  layer  in  thickness  on  the  sides,  but 
several  cells  thick  over  the  middle  part,  forming  a  thin  cushion. 
Rhizoids  are  developed  from  the  underside  near  the  smaller  (pos- 


Fig.  313- 

Germinating  spores  of 
Pteris,  aquilina  still  in  the 
sporangium. 


FERNS 


335 


terior)    end.     Among   these   are    the   sperm   cases   (antheridia). 
The  sperm  case  is  in  the  form  of  a  rounded  protuberance  from 


Fig.  314- 

Prothallium  of  fern,  underside,  showing   rhizoids,  antheridia   scattered  among  and  near 
them,  and  the  archegonia  near  the  sinus. 

the  underside  of  the  prothallium.     The  wall  consists  of  a  single 
layer   of    thin    cells.     The    central   portion  develops  a  number 


of 


sperms 


The 


sperms  are  coiled  in 
the  form  of  a  screw, 
with  numerous  deli- 
cate cilia  over  the 
smaller  end.  by  the 
vibration  of  which 
the  sperms  swim 
rapidly  for  a  half 
hour  or  so  in  the  wa- 
ter like  a  moving  screw.  The  egg  cases  (archegonia}  are  borne  also 

*  The  motile  sperms  of  plants  are  sometimes  called  "  anther ozoids." 


Fig.  315- 

Section  of  antheridia,  showing  sperm  cells,  and  sperms 
in  the  one  at  the  teft. 


336 


GENERAL   MORPHOLOGY   OF   PLANTS 


Fig.  316. 


on  the  underside  of  the  prothallium,  from  the  thicker  or  cushion 

portion,  since  they  are  larger  than  the  sperm  cases  and  need 

more  plant  food  for  their  own  growth, 
and  for  the  young  fern  embryo.  The 
egg  case  is  flask-  shaped,  the  venter 
sunk  in  the  tissue  of  the  prothallium, 
while  the  neck  projects  beyond,  and 
in  our  common  ferns  (Polypodiacea) 
curves  slightly  backward  toward  the 
small  end  of  the  prothallium.  When 
n-  the  spores  are  crowded  and  the  light 
is  very  weak,  so  that  they  get  but  little 

nutriment,  they  often  produce  only  protonemal  threads  which 

bear  only  sperm  cases.     On  the  normal  prothallia,  sperm  cases 

are  borne  only  on  the  young  prothallium,  while  the  egg  cases 

are  borne  later   on    the    older    tissue.      In  this   way  cross  fer- 

tilization is  usually  brought  about 

between  two    different  prothallia. 
505.   Fertilization.—  A  t    the 

time  the  egg  case  is  mature,  the 

cells    in    the    canal    of  the  neck 

dissolve    into    a    gelatinous   sub- 

stance,   which    oozes  out   at    the 

opening,  leaving  a  canal  down  to 

the  egg  in  the  venter.    The  sperm 

case    is    ruptured    by    absorbing 

water,  as  after  a  rain,  or  in  green- 

houses  when   they    are    watered. 

This    absorption    of    water    pro- 

Fig.  317- 

QUCeS     SUCh     a     pressure  that  the  Archegonium    of    fern.     Large  cell  in 

,          n     •      i        i  i  ,  the  venter  is  the  egg,  next  is  the  ventral 

terminal    Cell    IS    broken,  and  the  canal  ceil,  and  in  the  canal  of  the  neck 

.  .  are  two  nuclei  of  the  canal  cell. 

sperms  are  shot  out.    As  they  swim 

around  in  the  water  some  come  in  the  vicinity  of  an  open  egg  case 
(usually  of  another  prothallium),  are  more  or  less  entangled  in 
the  slime,  and  make  their  way  down  to  the  egg.  One  sperm  enters 
and  unites  with  the  nucleus  of  the  egg  and  completes  fertilization. 


FERNS 


506.   Development  of  the  embryo  fern  plant. — The  ferti- 
lized egg  is  the  beginning  of  the  second  generation  or  spore  plant 


Mature  and  open  archegonium  of  fern  (Adiantum  cuneatum)  with  sperms  making  their 
way  down  through  the  slime  to  the  egg. 

(sporophyte) ,  which  is  the  fern  plant  as  we  know  it.  The  egg 
divides  by  successive  divisions,  first  into  two  cells  and  then  into 
four.  These  four  cells,  or  quad- 
rants of  the  embryo,  give  rise  to 
four  parts  of  the  embryo.  The 
anterior  upper  quadrant  gives  rise 
to  the  stem,  the  anterior  lower  one 
to  the  leaf,  the  posterior  lower  one 
to  the  root,  and  the  posterior  upper 
one  to  a  haustorium-like  organ 
called  the  foot,  through  which  food 
substances  are  passed  from  the  pro- 
thallium  to  the  embryo  until  the 
latter  has  established  itself  on  the 
ground.  The  egg  case  grows  for  a 


Fig.   319- 

Two-celled  embryo  of  Pteris  serrulata. 
Remnant  of  archegonium  neck  below. 


time  with  the  embryo,  encloses  and  protects  it.  It  becomes, 
therefore,  a  hood  (calyptra).  The  root  grows  quite  rapidly, 
breaks  through  the  hood,  and  enters  the  ground.  The  leaf 


338 


GENERAL   MORPHOLOGY   OF   PLANTS 


breaks  through  later,  and  curves  upward  in  the  sinus  of  the  heart- 
shaped  prothallium,  and  takes  on  a  green  color  as  it  comes  to  the 
light.  The  stem  grows  more  slowly.  The  embryo  is  now  es- 
tablished and  the  prothallium  disappears,  though  it  remains 


Fig.  320. 

Embryo  of  fern  (Adiantum  concinnum)  still  surrounded  by  the  archegonium,  which  has 
grown  in  size,  forming  the  "calyptra."  L,  leaf;  5,  stem;  R,  root;  F,  foot. 

attached  to  the  young  fern  for  some  time.     As  the  fern  reaches 
the  age  for  spore  production  the  life  cycle  is  completed. 

507.  Dimorphism  in  ferns. — Some  ferns  have  two  kinds  of 
leaves,  that  is,  leaves  of  different  form,  each  kind  performing  a 
different  function  for  the  plant.  An  interesting  example  is  seen 
in  the  stag-horn  fern  (Platy cerium  alcicorne).  This  grows  in  the 
tropics  on  tree  trunks  quite  high  up  from  the  ground.  It  is 
often  grown  in  greenhouses  in  this  climate.  One  kind  of  leaf  is 
narrow,  and  branched  something  after  the  fashion  of  the  antlers 
of  a  stag.  These  leaves  are  either  fertile  or  sterile.  Another 
kind  of  leaf  is  broad  and  hugs  closely  against  the  base  of  the 
plant  and  the  tree  trunk.  Here  it  catches  falling  leaves  which 
decay,  hold  water  for  the  use  of  the  fern,  and  the  fern  roots  spread 


FERNS 


339 


through  the  decaying  mass  of  leaves  obtaining  also  some  food. 

Another  kind  of  dimorphism  is  present  in  several  of  our  common 
ferns.  Here,  as  in  the  sensitive  fern  (Onoclea 
sensibilis) ,  there  are  certain  leaves  with  large, 
expanded  green  blades.  These  perform  the 
function  of  photosynthesis.  Other  leaves  have 
stalks  (or  petioles)  equally  long,  but  the  blade 
of  the  leaf  is  very  much  contracted  and  the 
pinnae  inrolled.  These  are  the  fertile  leaves, 
and  bear  the  spore  cases  in  crowded  sori  within 
the  roll  of  the  pinnae.  The  vegetative  leaves 
arise  early  in  the  season,  while  the  spore-bear- 
ing leaves  (sporophylls)  are  developed  later, 
some  time  in  June.  Cutting  off  the  vegetative 
leaves  as  fast  as  they  appear  in  the  spring  will 
change  the  spore-bearing  leaves  to  vegetative 
ones>  and  many  of  them  will  be  intermediate 
between  the  two,  if  the  vegetative  leaves  are 


to  prothallium. 


Fig.  322. 
Staghorn  fern  (Platycerium  alcicorne). 


allowed  to  get  about  20-30  cm.  (8-12  inches)  high  before  they 
are  cut  off.     The  vegetative  leaves  will  need  then  to  be  cut  twice. 


340 


GENERAL   MORPHOLOGY   OF  PLANTS 


The  ostrich  fern  (O.  stmthiopteris  =  Matteuccia  struthiopteris)  pre- 
sents a  similar  dimorphism  of  the  leaves,  and  also  the  cinnamon 
fern  (Osmunda  cinnamomea) .  But  in  the  cinnamon  fern  the 
spore-bearing  leaves  are  formed  during  the  late  summer  and 
autumn.  They  are  hidden  in  the  crown  of  the  leaf  stalks  at  the 
end  of  the  stem  during  winter.  In  the  spring  they  elongate  and 
unroll  before  the  appearance  of  the  vegetative  leaves.  Parts  of 
the  spore-bearing  leaves  are  often  expanded  into  vegetative  parts. 
In  the  royal  fern  (O.  regalis)  the  dimorphism  is  shown  on  the 
same  leaf,  the  tips  of  the  divided  leaves  being  contracted  and 
bearing  spore  cases,  while  the  basal  portions  are  expanded.  In 
Clayton's  fern  (O.  claytoniana)  the  middle  part  of  the  leaf  bears 
the  spore  cases. 

508.   Apogamy  and  apospory.* — Some  ferns  have  developed 
the  habit  of  doing  away  with  certain  stages  in  their  life  history. 

For  example  Pteris  cretica, 
a  common  fern  grown  in 
greenhouses,  does  away 
with  the  sexual  organs 
and  fertilization.!  The 
fern  plant  (sporophyte) 
grows  directly  out  of  the 
tissue  of  the  prothallium 
(gametophyte) .  This  is 
called  apogamy,  which 
means  without  marriage. 
Some  other  ferns  can 
produce  prothallia  di- 
rectly from  the  leaves  without  the  spores.  This  is  apospory.  It 
is  not  a  rare  occurrence  in  the  common  brake,  though  the  pro- 
thallia never  become  more  than  protonemal  threads  in  this  fern. 
The  pinnae  which  bear  these  are  very  much  contracted  and  wrin- 
kled, and  can  be  easily  distinguished  from  the  normal  form  of 

*  For  reference. 

t  Recent  investigations  suggest  that  fertilization  here  takes  place  in  two 
adjacent  prothallial  cells  by  the  nucleus  migrating  from  one  into  the  other. 


Fig.  323. 
Apogamy  in  Pteris  cretica. 


FERNS  341 

the  fern.  When  the  sporophytes  of  the  sensitive  fern  are  forced 
to  grow  into  vegetative  leaves,  large  numbers  of  young  pro- 
thallia  are  formed  on  the  intermediate  leaves  in  place  of  the 
sporangia.* 

509.  Comparative  review  of  the  ferns. f — The  ferns  show  a 
striking  advance  in   the  evolution   of  the   sporophyte   over  the 
sporophyte  of  the  liverworts  and  mosses.     The  principal  features 
in  this  progress  or  higher  development  are  as  follows : 

First.  The  sporophyte  has  become  an  independent  plant  and 
can  obtain  its  own  food  without  the  aid  of  the  gametophyte, 
while  in  the  liverworts  and  mosses  it  is  dependent  on  the  game- 
tophyte. 

Second.  The  sporophyte  is  much  larger  in  size  and  differen- 
tiated in  form  into  roots,  stem  and  leaves. 

Third.  Its  structure  is  more  complex  with  highly  developed 
tissue  systems  for  aeration,  interchange  of  gases,  and  a  well- 
developed  vascular  system  for  the  transport  of  water  and  food. 

Fourth.  The  sporophyte  or  second  generation  has  become  the 
prominent  stage,  or  generation,  in  the  life  cycle  of  the  plant, 
whereas  the  first  generation,  the  gametophyte,  is  the  larger  and 
more  prominent  stage  in  the  liverworts  and  mosses. 

Fifth.  Another  evidence  of  the  advance  and  increasing  import- 
ance of  the  sporophyte  in  the  ferns  is  the  decrease  in  size  of -the 
prothallium  or  gametophyte,  which  is  much  smaller  than  the 
majority  of  the  gametophytes  of  the  liverworts  and  mosses. 

Sixth.  The  sporophyte  of  the  ferns  is  a  structure  better 
adapted  to  live  on  dry  land  and  to  obtain  great  size,  thus  enab- 
ling it  to  compete  successfully  over  all  the  lower  plants  because 
it  can  rise  above  them  to  obtain  the  light  relation. 

Seventh.  The  differentiation  of  the  leaves  in  some  species 
bringing  about  a  division  of  labor  between  vegetative  leaves 
and  spore-bearing  leaves  (sporophylls) . 

510.  Formula  for  life  history  of  the  f  eras.  $— The  game- 
tophyte is  the  prothallium  or  first  generation,  and  bears  the  sexual 

*  See  Chapter  XXVIII,  College  Botany,  by  the  author, 
f  For  reference.  J  For  reference. 


342  GENERAL   MORPHOLOGY    OF   PLANTS 

organs,  sperms  and  eggs;  the  fertilized  egg  develops  the  sporo- 
phyte,  the  fern  plant  which  bears  the  asexual  spores.  The  for- 
mula may  be  written  as  follows : 

Gametophyte  ^  )>  Fertilized  egg  —  Sporophyte  —  asexual 

spores  —  Gametophyte,  etc.     This  formula  abbreviated  is 
G—  <  S  >  FE  —  S  —  asp  —  G,  etc. 


Diagram  V.  Illustrating  the  life  cycle  of  a  fern  or  Pteridophyte.  Course  of  develop- 
ment follows  the  direction  indicated  by  the  arrows.  Zygote  equals  fertilized  egg.  Vegeta- 
tive multiplication  by  buds.  Note  the  increase  of  the  sporophyte  and  decrease  of  the 
gametophyte. 


CHAPTER   XXXIII. 
OTHER   FERN-LIKE   PLANTS. 

THE    HORSETAILS    (CLASS    EQUISETINE^). 

511.  General  characters. — The  horsetails  are  very  peculiar 
plants,  their  form  being  so  different  from  other  living  plants  that 
one  would  not  suspect  their  relationship  to  the  ferns  were  it  not 
for  the  method  of  spore  production,  and  the  characters  of  the 
prothallium  or  gamete  plant  (gametophyte) .  The  stems  possess 
the  chlorophyll  and  are  green,  with  stomates  in  the  epidermis, 
while  the  leaves  lack  chlorophyll.  The  stems  are  marked  with 
longitudinal  furrows  and  ridges  which  gives  them  a  fluted  appear- 
ance. The  stems  in  some  species  are  branched,  the  branches 
arising  in  whorls  at  the  nodes.  In  other  species  the  stems  are 
unbranched  as  in  the  scouring  rush  (Equisetum  hyemale) .  Their 
stems  are  well  infiltrated  with  silica  which  makes  them  rigid 
and  rough,  so  that  some,  as  the  scouring  rush,  have  been  used  to 
polish  certain  metal  work,  and  by  country  housewives  for  scour- 
ing kitchen  tables  and  floors.  The  stems  are  hollow  except  at 
the  nodes.  The  vascular  bundles  lie  beneath  the  ridges  and 
there  are  long  canals  which  lie  underneath  the  furrows.  There 
is  also  an  underground  stem  or  root  stock  from  which  the  aerial 
stems  arise.  At  the  nodes  are  membranous  sheaths  which  sur- 
round the  stem,  and  their  upper  edge  is  toothed.  These  sheaths 
represent  the  leaves;  they  are  devoid  of  chlorophyll,  photo- 

To  THE  TEACHER.  In  short  courses  or  first-year  courses  in  the  high 
school  it  may  not  be  practicable  to  study  any  of  the  plants  in  this  chapter. 
At  the  discretion  of  the  teacher  preserved  specimens  may  be  used  for  illus- 
tration. Horsetails,  club  mosses,  etc.,  may  be  seen  during  excursions,  and 
the  selaginellas  can  be  seen  in  some  greenhouses.  Where  more  time  is  allotted 
to  the  study  or  with  more  advanced  students  some  of  the  examples  described 
in  the  text  can  be  studied. 

343 


344 


GENERAL   MORPHOLOGY   OF  PLANTS 


synthesis  taking  place  in  the  green  stem.     The  fruiting  part  of 
the  stem  forms  a  spike  or  cone  at  the  apex  of  certain  stems. 

Most  of  the  species  of 
equisetum  grow  in  sandy 
places,  especially  along 
railroad  or  other  embank- 
ments, in  soil  where  few 
other  plants  grow.  This 
is  interesting  as  it  shows 
how  a  group  of  plants 
which  was  much  more 
abundant  in  the  past 
preserves  itself  from  ex- 
tinction by  being  adapted 
to  grow  under  conditions 
where  few  other  plants 
can.  Some  of  the  equi- 
setums,  however,  grow 
in  swamps  where  other 
vegetation  is  dense.  The 
genus  Equisetum  is  the 
only  genus  in  this  class. 
It  is  the  only  representa- 
tive of  a  class  of  plants 
which  flourished  in  geo- 
logical times  during  the 
"Carboniferous  Age." 

Fig.  325- 

Portion  of    Many  of  the  representa- 

fertile    plant  ,.  ... 

of     Equise-    tives  then  were   tree-like 

turn  arvense,       ,.  i    r        -i 

showing    forms,  and  fossil  remains 

whorls    of  -  i  •      .1  111 

leaves  and    are  found  in  the  coal  beds 

the     fruiting      ..  .  . 

spike.  formed     at     that     time. 


Fig.  324. 

Sterile  plant  of  horsetail   (Equi- 
setum arvense). 


There  are  now  about  twenty-five  living  species. 

512.  The  fruiting  spike  or  cone. — This  is  well  studied  in 
the  common  field  horsetail  (E.  arvense)  which  is  common  in 
damp  sandy  places  in  fields  and  along  railroads.  There  is  a^ 


OTHER  FERN-LIKE  PLANTS:  HORSETAILS         345 


extensive  underground  stem  which   is  much  branched.     Upon 

this  are   formed   two   kinds  of  aerial  shoots,  the 

fertile  and  sterile  shoots.     The  fertile  shoots  are 

formed  during  late  summer  and  autumn,  but  the 

stem    remains    short    during    the    winter.     Very 

early   in   the   spring   the   stem   elongates,   pushes 

above  the  ground,  and  the  spores  are  scattered. 

The    fertile    shoots    are    devoid    of    chlorophyll.         Fis-  326. 

,       ,          Peltate  sporophyll 

The  sterile  shoots  are  developed  all  through  the  of  Equisetum  (side 

.  view),  showing  spor- 

much    branched   and   green.     The  angia  on  under  side. 


summer,    are 


Fig.  327-  Fig.  328. 

Spore  of  Equisetum  with  Spore  of  Equisetum  with  elaters  uncoiled, 

elaters  coiled  up. 

r\ 

fruiting  spike  is  narrowly  cone- 
shaped  and  terminates  the  fertile 
stem.  The  spore-bearing  leaves 
(sporophylls)  are  peculiar,  being 
shield-shaped  with  a  short  stalk 
which  attaches  them  to  the  stem. 
They  are  in  crowded  circles  around 
the  stem,  and  thus  are  angular 
where  they  fit  against  one  another. 
Several  sac-like  spore  cases  (spor- 
angia) are  attached  to  the  inner 
face  around  the  short  stalk.  At 
maturity  the  axis  of  the  cone 
elongates,  the  spore  cases  crack 
open,  and  the  spores  escape.  The 

Male  and  femalV^t'eplantS,ofE?Mz-   Spores     have     a    Very     thick      wall. 

The  outer  layer  splits   into  four 


"hew?nnthSum  CshS  thin  bands  which  are  attached  to 
the  spore  at  one  point  and  wrapped 


346 


GENERAL   MORPHOLOGY   OF  PLANTS 


spirally  around  it.  These  uncoil  when  dry  and  coil  up  when 
wet.  This  aids  the  spore's  movement.  Several  are  often 
entangled  together  and  are  thus  enabled  to  form  a  small  colony 
of  prothallia  when  carried  away  by  the  wind. 

513.  The  gamete  plant  (gametophyte)   of  Equisetum.— 
When  the  spores  germinate  they  form  two  kinds  of  prothallia: 
some  produce  small  prothallia  with  only  sperm  cases  (antheridia) , 
while  others  produce  larger  prothallia  with  lobes,  and  egg  cases 
(archegonia)  situated  near  the  origin  of  the  lobes.     There  is  thus 
a  dimorphism  in  the  prothallia  of  Equisetum,  and  cross  fertiliza- 
tion is  enforced. 

THE    CLUB    MOSSES    (CLASS    LYCOPODINEvE). 

514.  The  lycopods,  or  large  club  mosses  (Lycopodium) . — 

These  plants  are  called  club  mosses  be- 
cause in  most  species  the  spore-bearing 
leaves  are  grouped  into  a  terminal  spike 
or  cone  (strobilus),  somewhat  resembling 
a  club,  and  because  the  small,  crowded 
leaves,  arranged  in  spirals  on  the  slender 
stems,  give  them  the  appearance  of  the 
leafy  stem  of  a  moss.     But  they  are  not 
true  mosses,  since  the  leafy  stem  of  the 
lycopods   is    a    spore  plant    (sporophyte) 
while  that  of  the  true  mosses  is  a  gamete 
plant    (gametophyte).       This 
may   help   us  to  understand 
why  the  leaves  and  stems  of 
the  mosses  and  liverworts  are 
not   true   leaves    and    stems, 
since   true  leaves  and  stems 
when  present  are  only  formed 
on  the  spore  plant  phase  of 


Fig.  330. 

Lycopodium  lucidulum,  bulbils  in  axils  of 
leaves  near  the  top,  sporangia  in  axils  of  leaves 
below  them.  At  right  is  a  bulbil  enlarged. 


plants.  The  lycopods  occur 
in  damp,  moist  situations,  usually  in  the  forest.  Some  of  them 
have  long,  creeping  stems  in  addition  to  the  upright  stems. 


OTHER  FERN-LIKE  PLANTS:   CLUB    MOSSES        347 

They  are  frequently  called  "  ground  pine,"  and  are  often  collected 
for  holiday  decorations.  The  branching  of  the  stems  is  usually 
forked.  Prothallia  are  not  known  in  northern  countries,  but  have 
been  found  for  several  species  in  tropical  countries.  In  one  of 
these  (L.  cernuum)  the  prothallium  is  a  cylindrical  body,  sunk  in 
the  earth,  with  green  lobes  at  the  top  where  the  sexual  organs  are 
developed.  In  others  the  prothallium  is  a  slender,  colorless, 
branched  body,  growing  saprophytically  in  the  decaying  bark  of 
trees.  With  some  of  these  a  fungus  is  associated,  making  a 
structure  similar  to  certain  mycorhizae  (paragraph  205).  In 
northern  countries  where  prothallia  have  not  been  discovered,  the 
species  propagate  by  vegetative  growth,  and  some  by  bulbils,  as 
in  the  case  of  L.  lucidulum.  These  bulbils  are  specialized  buds. 

515.  The  fruiting   spike   or  strobilus. — The   spore-bearing 
leaves  (sporophylls)  are  grouped  into  a  cylindrical  spike  (a  stro- 
bilus) at  the  end  of  the  stem  where  they  closely  overlap.     At  the 
base  of  each  sporophyll  is  a  spore  case  containing  many  small 
spores.     These  are  shed  by  the  spore  case  splitting  transversely. 
The  spores  are  produced  in  great  quantity  and  are  pale  yellow- 
ish in  mass.     They  are  sometimes  used  for  various  toilet  pur- 
poses, for  pyrotechnics,  and  for  coating  certain  pills  to  prevent 
adhesion. 

516.  The  little  club  mosses   (Selaginella). — Some  of  the 
species  of  Selaginella  in   northern    countries   resemble  Lycopo- 
dium,  and  are  sometimes  called  "little  club  mosses"  because  they 
are  much  smaller  in  size.     The  leaves  are  crowded  on  the  slender 
stems  and  in  many  species  are  arranged  in  four  or  six  rows. 
The  stems  of  many  species  are  dorsiventral,  the  rows  on  each 
side  being  approximated,  giving  a  flattened  appearance.     Many 
of  the  tropical  species  are  quite  large,  and  are  grown  in  green- 
houses for  ornament  because  of  the  beauty  of  their  form  and  the 
metallic  colors  of  some  species.     They  are  branched  profusely, 
often  in  a  single  plane,  thus  giving  the  appearance  of  a  large  leaf. 
One  of  the  tropical  species  is  known  as  "  resurrection  "  plant,  or 
"  resurrection  "  moss.     When  it  dries  it  rounds  up  in  a  ball. 
The  roots  are  thus  drawn  from  the  soil,  and  it  is  often  rolled 


348 


GENERAL   MORPHOLOGY   OF  PLANTS 


along  on  the  ground  by  the  wind.  With  the  advent  of  rains 
it  expands  and  becomes  green  and  fresh.  It  is  often  sold  in 
the  markets  because  of  this  curious  habit. 


Fig.  331-  Fig.  332.  Fig.  333.          Fig.  334. 

Selaginella  with  three  Fruiting      spike,  Large  spor-  Small  spor- 

fruiting  spikes.     (Sela-  showing   large  and        angium.  angium. 

ginella  apus.)  small  sporangia. 

517.  The    fruiting    spike    or    cone    of    Selaginella.— The 

sporophylls  are  usually  in  four  rows  over  the  end  of 
the  stems  and  branches,  making  a  four- sided  cone  or 


Fig.  335- 

Details  of  microspore  and  male  prothallium  of  Selaginella;  ist,  microspore;  2d,  wall  removed 
to  show  small  prothallial  cell  below:  3d,  mature  male  prothallium  still  within  the  wall;  4th, 
small  cell  below  is  the  prothallial  cell; the  remainder  is  antheridium  with  wall  and  four  sperm 
cells  within;  5th,  spermatozoid.  (After  Beliaieff  and  Pfeffer.) 

strobilus.  There  is  a  single  spore  case  at  the  base  of  each  sporo- 
phyll.  A  few  of  the  lower  ones  contain  each  a  few  very  large 
spores,  one  to  eight.  These  are  called  macrospores  *  or  mega- 

*  The  sporangia  which  produce  the  macrospores  are  called  macrospor- 
angia  or  megasporangia,  while  those  which  produce  the  microspores  are 
micros porangia. 


OTHER  FERN-LIKE  PLANTS:   CLUB    MOSSES       349 


spores,  which  means  large  spores.  The  upper  spore  cases  produce 
a  very  large  number  of  small  spores  (microspores] .  Since  the  spores 
are  of  different  sizes,  Selaginella  is  said  to  be  a  heterosporus  plant. 
A  plant  is  homosporus  when  the  spores  are  all  alike. 

518.  The  prothallia  or  gamete  plants  (gametophytes)  of 
Selaginella. — The  gamete  plants  of  Selaginella  are  diceceous  (or 
heterothallic] .  This  condition  of  the  prothallium  is  deter- 
mined in  the  spore.  The  small  spores  (microspores)  pro- 
duce small  male  gamete  plants.  There  is  only  one  cell 
in  the  prothallium  part.  The  other  cell,  which  is  larger, 
develops  into  the  sperm  case  with  a  wall  containing  a 
few  sperms.  The  sperms  are  biciliate,  as  they  are  in  the 
lycopods,  thus  being  different  from  those  of  the  ferns  and 
horsetails,  and  more  like  those  of  the  mosses.  The  large 


Fig.  336. 

Section  of  mature  macro- 
spore  of  Selaginella,  showing 
female  prothallium  and  arche- 
gonia.  (After  Pfeffer.) 


Fig.  337- 

Mature  female  prothallium  of 
Selaginella  just  bursting  open 
the  wall  of  macrospore,  expos- 
ing archegonia.  (After  Pfeffer.) 


Fig.  338. 

Seeding  of  Selagi- 
nella still  attached 
to  the  macrospore. 
(After  Campbell.) 


spore  (macrospore  or  megaspore)  develops  the  female  gamete 
plant.  This  never  escapes  from  the  spore  wall.  A  mass  of 
tissue  is  formed  which  cracks  open  the  spore  wall,  and  the  egg 
cases  (archegonia)  are  developed  in  the  exposed  surface.  There 
is  no  chlorophyll  in  either  male  or  female  prothallia.  This 
accounts  for  their  small  size,  the  larger  female  prothallium  being 
due  to  the  greater  amount  of  food  in  the  large  spore.  All  the 
food,  therefore,  for  the  gamete  plant  of  Selaginella,  comes  from 
the  spore  plant  (sporophyte)  and  was  stored  in  the  spores  while 


350  GENERAL    MORPHOLOGY   OF   PLANTS 

they  were  being  developed.  The  gamete  plants  of  Selaginella 
then  are  entirely  dependent  on  the  spore  plant  for  their  food,  a 
condition  of  things  entirely  different  from  that  in  the  other  fern 

plants  we  have  studied  and  in 
the  liverworts  and  mosses.  In 
one  species  of  Selaginella  (S. 
rupestris)  the  large  spores  some- 
times do  not  escape  from  the 
spore  case.  The  spore  case 
cracks  open  and  some  of  the 
small  spores  from  their  spore 
cases  above  fall  in.  Here  they 
produce  the  sperms,  and  the  egg 
in  an  egg  case  (archegonium)  is 
fertilized  while  the  female  gam- 
ete plant  is  still  in  the  spore 
case.  The  embryo  develops 
here  also,  and  when  the  root 
and  stem  emerge,  the  process  is 
exactly  like  that  of  a  germinat- 
ing seed  of  the  higher  plants. 
The  large  spore  case  of  Sela- 
ginella then  with  its  large  spore 
comes  very  near  being  a  seed, 
and  this  places  Selaginella  very 
near  the  seed  plants. 

THE    QUILLWORTS 
(ISOETES). 

519.  General   characters.— 

The     quillworts     are     peculiar 
Fig.  339-  plants.     They  grow  in  very  wet 

Isoetes,  mature   plant,    sporophyte  stage.    placeS)  or  even   partly   or   wholly 

submerged  for  parts  of  the  year.  The  leaves  are  long,  slender 
and  terete  except  at  the  base,  which  is  somewhat  spoon-shaped. 
The  bases  of  the  leaves  overlap  on  a  very  short  stem,  which  is 


OTHER   FERN -LIKE   PLANTS  351 

sometimes  broader  than  its  length.  The  leaves  are  thus  borne 
in  tufts.  The  roots  extend  from  the  lower  part  of  the  broad 
stem  (fig.  339).  There  are  two  kinds  of  spores,  large  and  small, 
and  both  kinds  of  gamete  plants  lack  chlorophyll.  The  quill- 
worts  resemble  certain  grasses  in  the  form  of  the  narrow  part  of 
the  leaf. 


COMPARATIVE    REVIEW    OF    THE    FERN    PLANTS.* 


520.  Relation  of  the  ferns  to  the  liverworts.— Although 
the  ferns  are  much  more  highly  organized  than  the  liverworts  it 
is  believed  that  they  have  had  their  origin  from  the  liverworts, 
that  is,  from  some  liverwort  which  existed  ages  ago 'but  which 
is  now  extinct.  Of  those  now  existing  the  horned  liverworts 
(Anthoceros)  come  nearest  this  supposed  ancestor  of  the  ferns. 
The  adder's  tongue  fern  (Ophioglossuni),  which  is  a  member  of 
the  class  to  which  the  true  ferns  belong  (Class  Filicinea],  is  one 
of  the  lowest  ferns  and  its  sporophyte  has  some  points  of  resem- 
blance to  that  of  Anthoceros.  In  the  adder's  tongue  fern  there  is 
a  simple  slender  stalk,  in  the  upper  end  of  which  the  spore  cases 
are  imbedded  and  separated  by  sterile  tissue.f  '  On  this  stalk 
there  is  a  simple  blade,  the  leaf.  This  is,  of  course,  far  from 
being  the  equivalent  of  the  sporogonium  of  Anthoceros  but  is 
more  like  it  than  is  the  sporophyte  of  any  other  of  the  fern  plants. 
It  suggests,  however,  that  it  may  have  been  derived  from  some 
Anthoceros-\ike  ancestor.  Other  members  of  the  order  (Ophio- 
glossales)  to  which  the  adder's  tongue  belong  have  divided  leaves, 
and  members  of  still  other  orders  which  cannot  be  described 
here  lead  up  to  the  condition  of  our  common  ferns,  from  massive 
and  simple  sporangia  to  the  specialized  sporangium  which  has 
been  described  for  the  common  ferns.  From  the  true  ferns 

*  For  reference. 

t  The  roots  of  the  adder's  tongue  and  of  other  members  of  the  order 
(Ophio gloss ales)  to  which  it  belongs  are  fleshy  and  have  a  fungus  in  their 
tissues,  thus  forming  a  mycorhiza  (see  paragraph  205).  The  prothallium  of 
the  members  of  the  order  is  a  degenerate,  tuberous  structure,  devoid  of 
chlorophyll  and  also  associated  with  a  fungus. 


352  GENERAL    MORPHOLOGY   OF  PLANTS 

(Class  Filicinece)  the  progression  has  gone  on  as  illustrated  by 
the  horsetails  and  the  club  mosses  until  a  condition  is  reached 
which  is  very  much  like  that  of  the  seed  plants.  The  principal 
things  which  have  been  developed  among  the  fern  plants  and 
which  mark  the  progression  above  the  liverworts  may  be  enume- 
rated as  follows: 

First.  The  sporophyte  has  become  an  independent  plant  by 
the  development  of  roots,  of  special  organs  for  assimilation 
(leaves),  and  of  a  well- developed  vascular  system  for  the  trans- 
port of  water  and  food  materials,  as  well  as  the  differentiation  of 
other  tissue  systems. 

Second.  Alternation  of  generations  has  reached  its  highest 
expression  in  that  both  generations,  the  gametophyte  and  the 
sporophyte,  can  live  as  independent  plants. 

Third.  Dimorphism  of  the  leaves  of  the  sporophyte  which 
results  in  a  division  of  labor  among  the  leaves  into  those  for  the 
function  of  photosynthesis  and  those  for  spore  bearing.  This 
was  begun  in  a  few  of  the  ferns,  becomes  the  rule  in  the  club 
mosses,  but  is  not  present  in  Isoetes. 

Fourth.  Heterospory,  the  development  of  two  kinds  of  spores 
large  and  small,  has  originated  in  the  higher  fern  plants.  This 
predetermines  the  sex  of  the  gametophytes  and  insures  cross 
fertilization  among  the  gametophytes,  which  is  a  distinct  advan- 
tage, and  is  one  of  the  characteristics  of  the  seed  plants.  This 
dimorphism  (or  heterothallic  condition)  of  the  gametophytes  is 
foreshadowed  in  the  true  ferns  where  varying  amounts  of  nutri- 
ment may  determine  the  sex  of  the  prothallia  and  is  almost 
wholly  determined  in  Equisetum.  In  Selaginella  and  Isoetes  't 
is  predetermined  in  the  spore. 

Fifth.  The  sporophyte  is  the  most  prominent  part  in  the  life 
cycle  of  fern  plants  and  is  better  adapted  to  existence  on  the  land. 
It  has  a  decided  advantage  over  the  gametophyte  generation  which 
is  especially  adapted  to  wet  or  moist  situations,  and  which  requires 
water  as  a  medium  for  conveying  the  sperms  to  the  egg.  The 
earliest  green  plants,  the  algae,  are  almost  exclusively  of  an 
aquatic  habitat.  The  sporophyte  of  the  fern  plants  being  per- 


FERN-LIKE   PLANTS   OF   CARBONIFEROUS    TIMES      353 

ennial  can  live  through  seasons  when  the  gametophytes  would 
perish.  Each  season  it  sheds  its  spores,  so  that  when  a  favorable 
period  arrives  the  gametophytes  develop  and  produce  new  sporo- 
phytes. 

Sixth.  The  gametophyte  decreases  in  size  and  importancs  as 
the  sporophyte  increases,  until  in  Selaginella  and  Isoetes  it 
becomes  entirely  dependent  on  the  sporophyte  for  its  nourish- 
ment. The  gametophytes,  it  is  true,  generally  become  free  from 
the  sporophyte,  but  not  until  sufficient  food  is  stored  up  in  the 
spore.  In  Selaginella  the  female  gametophyte  nearly  completes 
its  development  before  escape  from  the  sporangium,  and  in  some 
cases  actually  remains  in  the  sporangium  until  after  fertilization 
and  development  of  the  embryo,  thus  really  forming  a  seed  which 
is  the  special  character  of  the  seed  plants,  which  make  up  the 
highest  branch  of  the  plant  kingdom. 

Seventh.  The  supreme  position  which  the  sporophyte  was 
destined  to  occupy  in  the  plant  world  is  shown  in  the  luxuriance 
and  immense  quantity  of  vegetation  during  what  is  known  as  the 
coal  period,  or  Carboniferous  Age. 

521.  Deposits  of  coal  formed  by  the  fern-like  plants. — The 
fern  plants  occupy  a  very  minor  position  in  the  plant  world  at  the 
present  time  compared  to  their  dominant  position  in  past  ages. 
This  has  been  revealed  through  fossil  remains  of  plants  dis- 
covered in  different  strata  of  the  earth's  crust  and  through  the 
immense  deposits  of  coal  formed  during  what  is  known  as  the 
coal  period,  or  Carboniferous  Age.  The  coal  is  formed  by  plant 
remains  covered  by  other  strata,  and  subjected  to  such  great  pres- 
sure and  heat,  in  the  absence  of  air,  that  carbon  or  carbonized 
matter  is  formed  since  oxidation  cannot  ta';e  place.  The  coal 
is,  therefore,  laid  down  in  strata,  or  seams,  between  other  rock 
layers.  These  layers  of  coal  vary  from  one  to  three  meters  (three 
to  ten  feet)  in  thickness  in  most  of  the  regions  where  coal  is 
mined,  and  in  some  cases  is  much  thicker,  from  twenty  to 
thirty  meters  or  more  in  thickness.  The  pressure  which  is 
necessary  in  changing  plant  material  to  coal  reduces  enormously 
the  thickness  of  the  material,  so  that  it  would  require  beds  of 


354  GENERAL   MORPHOLOGY   OF   PLANTS 

plant  material  280-450  meters  thick  (900-1500  feet  in  thick- 
ness). In  the  United  States  there  are  several  hundred  thousand 
square  miles  of  coal-bearing  areas,  of  which  about  fifty  thousand 
are  worked.  This  gives  an  opportunity  to  see  what  an  enormous 
amount  of  vegetation  must  have  existed  during  that  age,  con- 
sidering the  fact  also  that  much  of  it  must  have  decayed  before 
the  geological  changes  occurred  which  submerged  the  material 
converted  into  coal.  In  the  coal  beds  very  little  of  the  plant 
remains  is  preserved  because  the  great  heat  consumed  them  and 
changed  them  largely  to  carbon.  But  numerous  impressions 
remain  which  enable  the  paleobotanist  to  determine  the  nature 
of  the  plants  which  flourished  on  the  earth  at  that  time.  These 
impressions  and  the  carbonized  remains  of  stems  are  more  evi- 
dent in  the  soft  coal,  but  evidences  are  also  found  in  the  hard 
coal  beds  to  indicate  that  they  also  are  the  remains  of  plants. 

522.  The  remains  of  the  fern  plants  found  in  the  coal  measures 
of  the  Carboniferous  Age  are  sufficient  to  show  that  the  number 
of  genera  and  species  was  far  greater  at  that  time  than  at  the 
present  day.  The  evidence  also  shows  that  they  were  much 
larger  in  size.  Besides  the  tree  ferns,  the  lycopods  were  of  tree 
size  as  were  the  closely  related  plants  Lepidodendron  and  Sigil- 
larii.  Equisetum-Yike  plants  called  Catamites  were  also  of  tree 
size.  There  were  also  many  other  tree  forms  which  are  extinct 
to-day.  There  was  much  more  moisture  and  carbonic  acid  in 
the  air  at  that  age.  This  probably  accounts  to  some  extent  for 
the  luxuriance  of  the  vegetation.  It  is  possible  that  the  greater 
amount  of  moisture  occasioned  large  areas  of  swampy  and  wet 
ground,  for  these  tree  forms  of  the  lycopods,  horsetails,  etc.,  flour- 
ished in  the  wet,  marshy  places.  This  may  have  led  to  a  condi- 
tion of  things  similar  to  the  peat  moors  of  the  present  day,  where 
decay  of  plant  parts  is  only  partial  and  the  firmer  parts  are 
even  preserved  from  decay.  In  this  way  the  deep  layers  of  plant 
material  may  have  accumulated,  and  later,  by  the  subsidence  of 
the  earth's  crust  at  these  points,  they  may  have  been  covered  with 
water  for  long  periods,  during  which  deposits  of  another  char- 
acter covered  them  which  later  formed  the  rock  stratum  overlying 


FERN-LIKE  PLANTS  OF   CARBONIFEROUS   TIMES      355 


GENERAL    MORPHOLOGY   OF  PLANTS 

the  coal  seams.  Alternate  elevation  and  subsidence  of  the  land, 
it  is  believed,  provided  for  the  superposed  strata  of  coal  and  other 
kinds  of  rock.  The  fern  plants  of  to-day  are  only  a  relic  of  the 
grand  fern  vegetation  of  the  Carboniferous  Age.  The  fern  plants 
have  gradually  lessened  in  importance  since  that  time,  both  in 
size  and  in  number.  From  being  the  dominant  vegetation  ele- 
ments of  that  time  they  now  occupy  a  subordinate  place,  while 
the  sporophyte  of  the  seed  plants  has  gradually  risen  to  be  the 
dominant  vegetation  element  first  represented  by  the  Gymno- 
sperms,  many  of  these  being  now  extinct,  and  now  represented  by 
the  Angiosperms  and  some  Gymnosperms.  It  is  an  interesting 
picture  to  represent  the  rise  and  fall  of  these  different  classes  of 
plants. 

523.  Formula  for  life  history  of  the  heterosporous 
Pteridophytes.*  —  The  formula  would  be  similar  to  that  for  the 
ferns,  but  with  two  kinds  of  spores  and  gametophytes.  It  will 
be  more  convenient  perhaps  to  start  the  cycle  with  the  sporo- 
phyte. Then 

'/  asexual  microspore  —  male  gametophyte  —  sperm  \  _ 
Sporophyte  C  ,  >  Fer- 

N  asexual  macrospore  —  female  gametophyte  —  egg  ' 


tilized  egg  —  Sporophyte,    etc.  =  S  <  ~_  FG  ~  *  >  FE  -  S.,  etc. 


*  For  reference. 


CHAPTER  XXXIV. 


THE   GYMNOSPERMS. 

524.  General  characters. — The  Gymnosperms  make  one  of 
the  two  large  classes  of  the  seed  plants  (Class  Gymnospernuz) . 
The  name  means  naked 

seeds,  the  seeds  being 
formed  on  the  outside  of 
a  modified  leaf  (sporo- 
phyll).  To  the  other 
class  belong  the  Angio- 
sperms  (Class  Angio- 
spermai) .  These  have 
their  seeds  enclosed  in 
a  pod-like  or  sac-like 
structure  formed  by  the 
infolding  of  a  modified 
leaf  (sporophyll). 

525.  The  cone-bear- 
ing  Gymnosperms.  — 
By  far  the  larger  num- 


Fig.  341- 
Cones  of  spruce  (Picea). 


ber  of  the  Gymnosperms  are  coniferous  (Order  Finales  or 
Coniferales  including  some  shrubs)  or  cone-bearing  trees,  the 
fruit  being  called  a  cone  because  of  its  form.  There  are  more 
than  three  hundred  species  of  conifers,  and  many  of  these  are 

To  THE  TEACHER.  One  of  the  pines  or  spruces  should  be  studied  care- 
fully if  it  has  not  already  been  done  in  Part  I.  The  cycads  in  conserva- 
tories may  be  pointed  out  as  fern-like  Gymnosperms,  and  where  trees  of 
gingko  are  growing  in  the  neighborhood  the  location  should  be  pointed  out 
to  the  students  and  a  branch  with  the  leaves  should  be  preserved  for  illus- 
tration. When  fruits  and  cones  can  be  obtained  they  should  also  be  studied. 
Cycas  sometimes  fruits  in  conservatories.  Zamia  can  be  obtained  from 
Florida.  More  advanced  classes  can  make  a  study  of  some  of  these  types.. 

357 


358 


GENERAL    MORPHOLOGY   OF   PLANTS 


trees  of  large  size  widely  distributed  over  different  parts  of  the 
world,  especially  the  Northern  Hemisphere.  Many  of  these 
grow  in  great  abundance  in  extreme  northern  latitudes  where 
the  winter  season  is  very  cold,  while  others  occur  in  temperate 
and  in  subtropical  countries  where  the  heat  of  the  season  is  often 
very  great.  Some  of  the  trees  of  great  size  are  the  giant  red 
woods  (Sequoia)  -of  the  Sierra  Nevada  Mountains.  Others  are 
the  pines,  spruces,  firs,  balsams,  larches,  cypresses,  cedars,  hem- 
lock spruces,  arbor  vitae,  etc.  The  American  yew  or  ground 
hemlock  is  an  example  of  a  shrubby  form.  The  majority  of  the 
conifers  have  a  straight  excurrent  trunk,  with  lateral  rather  subor- 
dinate branches,  thus  forming  a  large  straight  boll,  making  them 
especially  valuable  as  timber  trees,  aside 
from  the  valuable  quality  of  many  of 
the  woods.  The  branches  in  the  pines, 
balsams,  and  some  other  trees,  arise  in 
apparent  whorls  on  the  main  shoot, 
from  lateral  buds  grouped  just  below 
the  terminal  bud.  It  is  possible  then 
to  determine  the  age  of  the  tree  so 
far  as  the  branches  are  retained  over 
the  lower  part  of  the  trunk.  In  the 
hemlock  spruce,  cedars,  and  some  others 
the  branches  are  more  or  less  scattered 
along  on  the  trunk. 

526.  The  leaves  are  needle-like  and 
quite  long  in  the  pines,  shorter  and 
more  flattened  in  the  spruces,  and  scale- 
like  in  the  cedars,  arbor  vibe,  etc.  In 
the  pines  they  are  in  clusters  of  two 
to  five  (rarely  one  in  some  western 
Pines)  at  the  end  of  a  very  short  branch. 

Q    k;nds     Qf 


Fig.  342. 


wood-cells.    X325.    (After  Sachs.) 

developed  each  year,  the  long  ones  and  the  short  ones.  The  long 
ones  correspond  in  arrangement  on  the  stem  to  the  short  ones 
and  this  is  the  reason  they  are  so  crowded  on  the  stem  as  to 


THE   GYMNOSPERMS  359 

represent  a  whorl.  The  leaves  are  hard  and  firm,  have  a  thick 
rather  resinous  cuticle,  and  a  thick  epidermis.  Underneath  the 
epidermis  are  a  few  layers  of  stony  (sclerenchyma)  cells  inside 
of  which  is  the  thin-walled  chlorophyll-bearing  parenchyma  with 
fluted  cell  walls.  There  are  one  or  two  vascular  ducts  in  the  leaf 
according  to  the  species,  besides  the  resin  ducts.  This  structure 
of  the  leaves,  together  with  their  small  and  compact  size,  fits  them 
to  withstand  the  drying  effect  of  cold  winters,  the  heat  of  the  sun 
and  severe  droughts  in  summer.  Some  of  the  conifers  are  de- 
ciduous, as  the  bald  cypress,  larch,  etc. 

527.    The  structure  of  the  stem  and  its  development  is  much  as 
described  for  woody  stems  (paragraphs  96-100)  but  there  are  no 


Fig.  343- 
Staminate  cones  of  American  yew  (Taxus  canadensis). 

trachea  in  the  vascular  system,  these  being  represented  by  trache- 
ides  similar  to  the  trachea  but  their  cross  walls  not  being  per- 
forated. The  most  characteristic  feature  of  the  wood  is  the 


360  GENERAL   MORPHOLOGY   OF   PLANTS 

presence  of  the  "  bordered  pits  "in  the  wood  cells  which  appear 
like  minute  openings  in  a  bordering  circle,  in  one  view,  and 
elliptical  in  edge  view  (fig.  342),  the  large  pits  being  on  either 
side  of  a  middle  partition,  each  with  a  minute  opening  on  the 
outside.  Resin  ducts  also  occur  in  the  wood.  The  fruit  of  the 
conifers  is  mostly  a  cone  fruit,  the  seeds  being  borne  on  the  inner 
face  of  scales  which  are  united  around  an  axis  in  the  form  of  a 
cone.  In  the  ground  hemlock  or  American  yew,  the  fruit  is  a 
berry  with  a  red  pulp,  but  here  the  pollen-bearing  sporophylls 
are  arranged  in  the  form  of  a  cone  called  the  staminate  cone, 
much  as  they  are  in  all  of  the  cone-bearing  Gymnosperms. 

LIFE    HISTORY    OF    THE    PINE. 

528.  The  staminate  cones  and  pollen. — The  staminate  cones 
are  borne  in  clusters  at  the  ends  of  branches  occupying  the  posi- 
tion of  a  whorl  of  branches.  Each  cone  consists  of  a  short  axis 

covered  by  short  scale-like  structures . 
compactly  arranged  in  a  spiral  manner. 
Each  one  of  these  scales  is  a  modified 
leaf,  or  sporophyll.  Upon  the  under- 
side are  two  sacs  which  open  by  a  slit 
at  maturity  and  scatter  the  pollen.  All 
in  a  cone,  or  cluster  of  a  cone,  usually 
open  suddenly  and  simultaneously, 
emitting  a  cloud  of  the  pollen.  The 
pollen  is  so  abundant  that  it  some- 
Fig.34*  times  falls  as  it  were  in  "showers," 

S'SJSlJ&      covering    leaves,    etc.,    with     a    thin, 
yellow-looking      powder,     resembling 

"  flour  of  sulphur."  The  scales  are  called  stamens,  hence  the 
name  staminate  cone.  The  pollen  grains,  however,  are  developed, 
four  from  each  mother  cell,  precisely  as  the  spores  are  developed 
in  the  spore  cases  of  the  ferns,  mosses  and  liverworts.  The 
pollen  grains  are,  therefore,  small  spores  (microspores) ,  the  anther 
sacs  are  small  spore  cases  (micro sporangia)  and  the  stamens  are 
small  spore-bearing  leaves  (microsporophylls) .  The  pollen  grain 


THE  GYMNOSPERMS 


361 


of  the  pines,  spruces,  etc.,  has  a  peculiar  structure.  The  pollen 
grain  has  on  either  side  two  rounded  air  sacs  formed  by  a  swelling 
out  at  these  points  of  the  outer  layer  of  its  wall.  These  serve  as 
floats,  and  the  pollen  grains  are  very  buoyant,  being  carried  great 
distances  by  air  currents.  The  mature  pollen  grain  is  a  rudi- 
mentary male 
prothallium  or 
gamete  plant 
(gametophyte) . 
While  it  is  de- 
veloping two 
sterile  prothal- 
lial  cells  are 
formed  which 
soon  disappear 
in  the  pines. 
The  rest  of  the 

Fig.  346.  Fig.  347- 

Section  of  staminate        Two     sporo-  pollen    grain    is 
cone,   showing   sporan-     phylls  removed, 

gia.  showing  open-  a   rudimentary 

ing     of     spor- 
angia, sperm  case  (an- 

theridium)  and  consists  of  two  cells,  the  tube  cell  (or  wall 
cell)  and  the  sperm  case  cell  (antheridial  cell),  or  central  cell 
(see  fig.  348). 

529.  The  pistillate  cone  and  ovules.  — The  pistillate  cone 
(or  carpellate  cone)  forms  the  fruit.  These  cones  are  also  usually 
developed  in  clusters.  They  are  developed  from  a  whorl  of  buds 
at  the  end  of  the  shoots.  They  begin  their  development  in 
spring,  and  the  axis  is  soon  covered  with  spirally 
arranged  scales.  On  the  inner  and  upper  face 
of  each  scale,  at  its  base,  are  two  ovules  which 
correspond  to  large  spore  cases  (macrospor- 
angia).  At  the  lower  end  are  two  horn-like 
processes,  and  between  these  is  an  opening, 
the  micropyle.  The  wall  of  the  ovule  is  called  the  integu- 
ment. The  interior  tissue  of  the  ovule  is  called  the  nucellus. 
It  is  in  truth  the  real  tissue  of  the  large  spore  case.  A  large 


Fig.  345- 

Stamina te  cone  of  white 
pine,  with  bud  scales  re- 
moved on  one  side. 


Fig.  348. 

Pollen      grain     of 
white  pine. 


362 


GENERAL   MORPHOLOGY   OF   PLANTS 


spore  (macrospore)  is  formed  inside,  which  never  escapes,  but 
develops  the  female  prothallium  or  gamete  plant 
(gametophyte) ,  which  in  the  Gymnosperms  is  known 
as  the  endosperm.  In  this  prothallium,  egg  cases 
(archegonia)  are  formed  near  the  micropyle,  each 


Fig.  349- 

Section  of  female 
cone  of  white  pine, 
showing  young  ovules 
(macrosporangia)  at 
base  of  the  ovuliferous 
scales. 


Fig.  350. 

Scale  of  white  pine  with 
he  two  ovules  at  base  of 
ovuliferous  scale. 


Fig.  35i- 

Scale  of  white  pine  seen 
from  the  outside,  showing 
the  cover  scale. 


containing  a  large  egg  which  is  surrounded  by  a  regular  layer 
of  cells,  the  wall  of  the  venter,  called 
jacket  cells,  or  a  jacket.  After  fertiliza- 
tion the  embryo  is  developed  within 
the  ovule.  The  ovule  together  with 
the  endosperm  and  embryo  forms  the 
seed.  The  scales  have  become  large 
and  hard.  It  requires  about  fifteen 
months  from  the  time  of  pollination 
(during  May)  to  the  ripening  of  the 
sp*  seed  (August  of  the  following  year). 
Soon  after  the  ripening  of  the  seed, 
the  cone  dries.  As  this  takes  place 
the  seed  with  a  thin  layer  of  the 
scale,  in  the  shape  of  a  knife  blade, 
splits  off  from  the  scale.  The  pine 
seed,  therefore,  is  a  "  winged  "  seed. 
530.  Pollination  and  fertilization. — At  the  time  the  pollen 

is  scattered  the  small  pistillate  cones  stand  erect,  with  the  scales 


..a" 


Fig.  352. 

Macrosporangium  of  pine 
(ovule),  int,  integument;  «, 
nucellus;  m,  macrospore;  pc, 
pollen  chamber;  pg,  pollen 
grain;  an,  axile  row;  fpl, 
spongy  tissue.  (After  Fer- 
guson.) 


THE  GYMNOSPERMS 


363 


spread  apart.  They  thus  catch  the  flying  pollen,  which  falls 
down  to  the  base  of  the  scales  and  is  caught  in  a  drop  of  a 
viscid  substance  exuded  through  the  micropyle  of  the  ovule. 
When  this  dries  it  draws  the  pollen  grains  up  in  the  micropyle 
close  against  the  nucellus.  The  scales  now  close,  and  the  cone 
turns  downward,  in  which  position  the  ovules  are  better  pro- 


Fig.  353- 

Section  of  ovule  of  white  pine,  int,  integu- 
ment, pc,  pollen  chamber;  pt,  pollen  tube;  n, 
nucleus;  m,  macrospore  cavity. 


Fig-  354- 

Last  division  of  the  egg  in  the  white 
pine  cutting  off  the  ventral  canal  cell  at 
the  apex  ot  the  archegonium.  End, 
endosperm;  Arch,  archegonium. 


tected  from  rain  and  outside  changes  in  the  air.  The  scales 
become  further  sealed  with  resin.  This  occurs  in  May  or  June. 
The  pollen  grain  then  germinates,  the  tube  cell  forming  a  tube 
which  penetrates  the  nucellus,  and  usually  branches,  feeding  on 
the  disintegrated  cell  contents,  and  quantities  of  starch  grains  are 
found  in  the  pollen  tube.  During  this  process  the  central  cell  of 
the  sperm  case  divides  into  two  cells;  one  is  sterile,  while  the 


GENERAL   MORPHOLOGY   OF  PLANTS 


B.  C.  D.  E. 

Fig.  355- 

White  pine,  showing  details  of  mature  scales  and  seed.  A.  Sterile  scale,  seeds  undeveloped. 
B.  Scale  with  well-developed  seeds,  c.  Seeds  have  split  off  from  scale.  D.  Back  of  scale 
with  small  cover  scale.  E.  Winged  seed  free  from  scale. 


Fig.  356. 


Branch  of  white  pine,  showing  young  female  cones  at  time  of  pollination  on  the  ends  of  the 
branches,  and  one-year-old  cones  below,  near  the  time  of  fertilization. 


THE  GYMNOSPERMS 


36S 


other  becomes  a  sperm  mother  cell,  called  the  generative  cell  or 
the  body  cell.     These  cells  move  along  in  the  apex  of  the  tube. 

The  pollen  tube  rests  in 
the  nucellus  during  win- 
ter. The  following  spring 
it  begins  growth  again, 
and  the  nucleus  of  the 
generative,  or  body,  cell 
divides  into  two  sperm 
nuclei  in  the  one  cell. 
The  female  prothallium 


Fig.  357- 

Pollen  grains  of    pine,    one   of  them    germinating. 
p1  and  p2,    the  two  disintegrated  prothallial   cells   = 
sterile  part  of  male  gametophyte;  a.c.,  central  cell  of  an-     m 
theridium;  v.n.,  vegetative  nucleus  or   tube  nucleus  of 
the  single-wall  cell  of  antheridium;  s.g.,  starch  gi 


«; 
lb 


cr»nrp» 
SP°re 

lus),  and  when  the   egg 
cases  are  mature  the  pol- 


Fig.  358. 

Section  of  nucellus  and  endosperm  of 
white  pine.  The  inner  layer  of  cells 
of  the  integument  shown  just  outside  of 
nucleus;  arch,  archegonium;  en,  egg  nu- 
cleus. In  the  nucellar  cap  are  shown 
three  pollen  tubes :  vn,  vegetative  nucleus 
or  tube  nucleus;  sic,  stalk  cell;  spn,  sperm 
nuclei  (the  larger  one  in  advance  is  the 
one  which  unites  with  the  egg  nucleus). 
The  archegonia  are  in  the  endosperm  or 
female  gametophyte.  (After  Ferguson.) 


Fig.  359- 

Archegonium  of  white  pine  at  stage  of  fertili- 
zation, en,  egg  nucleus;  spn,  sperm  nucleus  in 
conjugation  with  it;  nb,  nutritive  bodies  in 
cytoplasm  of  large  egg;  cpt,  cavity  of  pollen 
tube;  vn,  vegetative  nucleus  or  tube  nucleus; 
sc,  stalk  cell;  spn,  second  sperm  nucleus;  pr, 
portion  of  prothallium  or  endosperm;  sg,  starch 
grains  in  pollen  tube.  The  sheath  of  jacket 
cells  of  the  archegonium  is  not  shown.  (After 
Ferguson.) 


366  GENERAL   MORPHOLOGY    OF   PLANTS 

len  tube  makes  its   way  into    the  neck  end   of  an    egg   case, 
and  empties  the  cells  and  sperms  into  the  cytoplasm  of  the  egg 
(%•   359)-     The    larger    sperm    (which    was   in 
advance  in  the  pollen  tube)  unites  with  the  egg 
30      nucleus,  and  without  any  resting  stage  the  fer- 
tilized egg  nucleus  at  once  divides  into  two,  and 
these  into  two  more.     These  four  nuclei   move 
to  the  base  of  the  egg  case,  and  there  by  suc- 
cessive divisions  organize  the  embryo,  which  is 
Pine  seed,  section  pushed  down  into  the  mass  of  the  endosperm  by 

of.      sc,  seed  coat;  n,  ,    •          r    .,  n       .        .,  1-11 

remains  of  nuceijus;  certain  or  its  cells  in  the  rear,  which   elongate 
female  gam<5ophyte7;  rapidly  and  are  called  the  suspensor.     The  seed 

emb,  embryo  =  young      •  -\    .  -,  .    ,          r    ,,  , 

sporophyte.  Seed  co.it  ripens  in  late  summer  and  consists  of  the  seed 


sporo-  coats  (coats  of  the  ovule),  the  remnants  of  the 
nucellus,   the  endosperm   and  embryo  with    its 
rudimentary  root,  stem  and  leaves.     In  the  germination  of   the 
seed  (paragraph  13)  and  establishment  of  the  young  pine  plant 
the  life  history  is  completed. 


OTHER    GYMNOSPERMS.* 

531.  The  Cycads. — The  other  most  prominent  class  of  the 
Gymnosperms  is  made  up  of  the  cycads  (order  Cycadales) .  These 
are  mostly  tropical  or  subtropical  plants,  but  some  are  often 
grown  in  greenhouses,  especially  the  Cycas  revoluta,  sometimes 
incorrectly  called  sago  palm  f  on  account  of  its  trunk  and  large 
spreading  leaves  at  the  apex,  giving  it  the  aspect  of  the  tree  palms, 
and  because  of  a  coarse  starchy  material  obtained  from  the  stem 
called  Japanese  sago.  Some  of  the  cycads  like  Zamia  (there  are 
several  species  in  Florida)  have  tuberous-like  trunks.  The  leaves 
are  large,  stiff  and  feather-like  because  of  their  narrow,  pinnate 
divisions,  and  resemble  the  leaves  of  some  of  the  tree  ferns.  In 
their  fructification  they  bear  a  striking  resemblance  to  the  ferns, 
and  stand  lower  in  grade  of  classification  than  the  conifers. 

*  For  special  assignment  or  reference. 

f  The  sago  palm  is  Metroxylon  Icevis  and  M.  rumphii  of  the  East  Indies 
(Chapter  XXXVI). 


THE  GYMNOSPERMS 


367 


.  361 


A  cycad  (Cycas  revoluta),  showing  cluster  of  fertile  leaves  (macrosporopbylls)  in  the  center. 


Fig.  362. 

A  sporophyll  (stamen)  of  cycas;  sporangia  in 
groups  on  the  underside,  b,  group  of  sporangia; 
c,  open  sporangia.  (From  Warming.) 


Fig.  363. 

Macrosporophyl!  of  Cycas 
revoluta. 


368 


GENERAL   MORPHOLOGY   OF   PLANTS 


532.  Cycas. — In  cycas  the  small  spore-bearing  leaves  (micro- 
sporophylls)  are  flattened  leaves  with  true  sporangia,  similar  to 
the  spore  cases  of  some  of  the  ferns,  scattered  over  the  under 


Fig.  364- 
Macrosporangiumof  Cycas  revoluta. 


Fig.  365- 

Roentgen  photograph  of  same,  show- 
ing female  prothallium. 


surface  of  the  leaves.  These  contain  the  small  spores  (micro- 
spores)  (fig.  362).  The  female  plants  have  the  large  spore- 
bearing  leaves  (macrosporophylls,  or  megasporophylls) .  These 

are  produced  at  certain  seasons  in 
a  rosette  near  the  apex  of  the  stem. 
Each  spore-bearing  leaf  is  shaped 
like  the  ordinary  leaves,  with  numer- 
ous pinnate  divisions,  but  they  are 
much  smaller,  lack  chlorophyll,  and 
Fig.  366.  are  very  hairy  or  woolly  with  pale 

sinl^^ie'at^eilUlulLwTnTthe      yellowish  brown  hairs.     The  large 

spore   cases    (macrosporangia) ,    or 

ovules,  are  borne  on  either  side  of  the  leaf  near  the  base,  one  each 
in  place  of  a  pinna.  When  they  are  ripe  they  resemble  a 
stone  fruit  with  a  fleshy  exocarp,  a  stony  endocarp,  and  the 
meat  or  kernel  within  is  the  female  prothallium  or  endo- 
sperm (fig.  365). 


THE  GYMNOSPERMS 


369 


533.  Zamia.  —  Zamia  is  also 
dioecious,  and  the  male  and  female 
plants  both  bear  cones.  In  the 
staminate  cones  (fig.  366)  the  spore- 
bearing  leaves  are  short  and  stout, 


Fig.  367. 
Pistillate  cone  of  Zamia. 


Fig.  368. 

Zamia,  one  scale  of  the  pistillate  cone,  showing 
the  two  ovules. 


somewhat  triangular  wedge-shaped,  and  very  closely  crowded. 
Upon  the  underside  are  numerous  small  oval  spore  cases  similar 
to  those  of  cycas  and  some  of  the  lower  ferns,  which  contain 
numerous  small  spores.  The  pistillate  or  carpellate  cone  is 
similar  in  external  appearance  but  larger.  The  spore-bearing 
leaves  are  similar  in  form  but  bear  two  large  spore  cases,  one 
on  either  side  but  covered  by  the  broadened  outer  end. 

534.  Life  history  of  the  cycads. — The  life  history  of  the 
cycads  presents  many  interesting  features,  but  the  account  here 
must  be  very  brief.  The  pollen  grain  (microspore)  is  a  rudi- 
mentary male  prothallium  as  in  the  pine,  but  some  of  the  sterile 
prothallial  cells  persist  in  the  mature  small  spore  (microspore). 
After  pollination  the  tube  cell  grows  down  into  the  tissue  of  the 
nucellus  (in  Zamia)  at  one  side  of  the  endosperm  forming  a 
haustorium  which  supplies  the  generative  cell  with  food.  The 
pollen  end  of  the  tube  then  bends  down  into  a  cavity  in  the 


370 


GENERAL    MORPHOLOGY    OF   PLANTS 


nucellus  which  is  filled  with  a  fluid  and  lies  next  the  egg  cases  in 
the  female  prothallium  (endosperm).     The  central  cell  (or  stalk 


Fig.  369- 

A,  section  of  ovule  of  zamia,  partly  diagrammatic,  showing  germinating  pollen  tubes 
entering  the  nucellar  cap.  M,  micropyle;  O,  outer  portion  of  ovule  (exocarp);  /,  inner 
stony  portion  of  ovule  (endocarp) ;  PC,  pollen  chamber;  N,  nucellar  cap;  P,  endosperm  (pro- 
thallium);  ;4,archegonium  (pollen  grains  in  pollen  chamber  are  germinating,  the  pollen  tubes 
growing  in  the  tissue  of  the  nucellar  cap).  B,  same  a  little  later,  showing  basal  end  of  the 
pollen  tubes  bending  downward  as  the  sperm  cells  in  that  end  are  developing. 

cell  sometimes  called)  has  divided,  as  in  pines,  into  a  sterile  cell 
and  a  generative  cell  (body  cell)  which  now  divides  into  the  two 
sperm  cells,*  which  are  oval  in  form,  and  each  has  a  spiral  band 
of  numerous  cilia  around  the  smaller  end  (fig.  373).  Some  of 


Fig.  370. 

Zamia.  A,  mature  pollen  grain  showing  within,  the  tube  cell  at  the  right,  the  central 
cell  in  the  middle,  the  prothallial  cell  at  the  left;  B,  beginning  of  germination  of  pollen 
grain;  C,  farther  stage  in  the  germination  of  pollen  grain,  the  tube  nucleus  of  cell  moving  into 
the  tube.  (After  Webber.) 

these  sperms  swim  into  the  egg  cases,  one  unites  with   an  egg 
nucleus,  and  the  embryo  is  then  formed,  thus  making  a  seed. 

*  Two  sperm  cells  are  formed  in  most  cycads  as  in  other  seed  plants,  but 
in  Microcycas  there  are  eight  generative  cells,  each  of  which  divides  to  form 
two  sperms,  making  sixteen  in  all  for  each  small  spore. 


TIL K  G YMNOSPERMS 


371 


On  the  germination  of  this  and  the  establishment  of  the  Zamia 
plant  the  life  history  is  complete. 

535.     Gingko. — Gingko  (Gingko   biloba)    is   a   very   interest- 
ing tree.     It  is  a  native  of  China  and  is  now  widely  grown  in 


Fig.  372- 

Sperms  of  zamia  in 
pollen  tube;  pg,  pollen 
grain;  aa,  sperms. 
(After  Webber.) 


Fig.  373- 

Sperm  of  zamia,  show- 
ing spiral  row  of  cilia. 
(After  Webber.) 


Fig.  371- 

Zamia.  Germinating  pollen 
grain  in  more  advanced  stage, 
the  pollen  tube  with  nucleus  of 
tube  cell  not  shown.  The  cen- 
tral cell  has  divided  into  two 
cells;  the  one  at  the  left  is  the 
generative  or  body  cell  preparing 
to  divide  into  the  two  sperms. 
The  prothallia  cell  at  the  left  is 
growing  out  into  the  other  cell 
(stalk  cell)  derived  from  the 
division  of  the  central  cell. 

Europe,  America,  and  other  countries,  as  an  ornamental  tree. 
It  is  the  sole  survivor  of  a  group  of  plants  which  were  very 
abundant  in  geological  times.  The  leaves  are  triangular,  radi- 
ately  veined,  and  resemble  in  form  the  pinnules  of  the  maiden 
hair  fern  (Adiantum),  The  -large 
spore  cases  form  a  fleshy  fruit,  about 
the  size  of  a  plum,  with  a  soft  exocarp 
and  a  stony  endocarp,  the  meat  within 
being  the  female  prothallium  or  endo- 
sperm. There  are  motile  sperms, 
and  the  life  history  is  similar  to  that 
of  the  cycads. 

536.   Comparative  review  of  the 
' — The  lowest  Gym- 


Fig- 374- 

Gingko  biloba,  end  of  stem  with 
spray  of  leaves  and  two  fruits. 

nosperms  are  represented    by    the    cycads.     They  bear  certain 
resemblances  to  the   ferns,  which    indicate   that  they  have   had 
their  origin  from   some  fern-like   ancestors  which  are  not   now 
known.     These  resemblances  are  as  follows : 
First,  the  form  of  the  leaves. 

*  For  reference. 


3/2  GENERAL    MORPHOLOGY   OF   PLANTS 

Second,  the  arrangement,  structure  and  dehiscence  of  the 
microsporangia  which  are  very  much  like  the  sporangia  of  some 
of  the  lower  families  of  the  true  ferns. 

Third,  the  motile  sperms. 

Fourth,  the  form  and  development  of  the  female  pro- 
thallium  with  its  archegonia  which  recalls  that  of  Selaginella. 
In  this  respect  the  conifers  also  resemble  the  higher  Pterido- 
phytes. 

The  progress  in  evolution  made  by  the  Gymnosperms  over  the 
Pteridophytes  may  be  briefly  stated  as  follows: 

First.  The  establishment  of  heterospory  and  the  permanent 
division  of  labor  between  the  two  kinds  of  sporophylls,  which 
was  introduced  by  some  of  the  higher  Pteridophytes.  This 
division  of  labor  is  even  extended  further  in  some  species, 
as  in  the  cycads  where  the  microsporophylls  bearing  pollen 
grains  (microspores)  are  on  different  plants  (male)  from  the 
macrosporophylls  bearing  the  ovules,  which  are  on  female 
plants. 

Second.  The  complete  division  of  labor  between  sporophylls 
for  the  production  of  spores,  and  vegetative  leaves  for  the  chlo- 
rophyll function. 

Third.  The  aggregation  of  the  sporophylls  into  groups,  which 
was  also  initiated  by  the  higher  Pteridophytes. 

Fourth.  The  more  specialized  development  of  tissue  systems, 
the  growth  of  the  parts  of  the  sporophyte  by  a  group  of 
meristem  cells  instead  of  growth  by  a  single  apical  cell. 

Fifth.  The  increasing  prominence  and  importance  of  the 
sporophyte  and  decreasing  prominence  of  the  gametophyte. 

Sixth.  The  lessening  in  the  size  of  the  gametophyte,  especially 
in  the  reduction  of  the  archegonia,  the  neck  being  smaller,  and 
the  reduction  of  the  male  prothallium  so  that  there  are  very  few 
or  no  prothallial  cells,  while  the  wall  of  the  antheridium  has 
almost  completely  disappeared,  the  tube  cell  alone  remaining, 
and  the  number  of  sperm  cells  is  greatly  reduced.  (In  Mycro- 
cycas,  however,  there  are  sixteen  sperm  cells,  about  half  the 
number  common  in  a  great  many  Pteridophytes.) 


THE   GYMNOSPERMS  3/3 

Seventh.  The  complete  dependence  of  the  gametophytes  on  the 
sporophytes,  which  also  was  introduced  by  the  higher  Pterido- 
phytes  but  in  the  Gymnosperms  has  been  carried  farther,  the 
female  prothallium  never  escaping  from  the  ovule  or  macro- 
sporangium.  The  female  prothallium,  or  endosperm,  is  parasitic 
in  the  nucellus  of  the  ovule  (macrosporangium),  for  when  it  is 
mature  the  nucellus  is  nearly  or  quite  consumed;  only  a  papery 
remnant  surrounds  the  endosperm. 

Eighth.  The  introduction  of  pollination,  necessitated  by  the 
fact  that  the  female  prothallium  does  not  escape  from  the  ovule 
and  is  separated  from  the  outside  by  the  nucellus  tissue,  i.e.,  a 
part  of  the  ovule  or  macrosporangium.  The  pollen  or  micro- 
spores  must  be  transported  to  the  ovule. 

Ninth.  The  germination  of  the  tube  cell,  or  wall  cell  of  the 
antheridium  to  form  the  pollen  tube,  which  penetrates  the 
nucellus  tissue  in  the  case  of  the  cycads  and  Gingko  to  provide 
nutriment  for  the  development  of  the  motile  sperms,  which  then 
swim  from  the  pollen  chamber  into  the  archegonia,  while  in  the 
conifers  the  pollen  tube  penetrates  the  nucellus,  and  obtains 
nutriment  for  the  same  purpose,  but  makes  its  way  directly  into 
the  archegonium  into  which  it  then  empties  the  sperm  cells. 
The  pollen  tube  is  thus  parasitic  in  the  nucellus,  for  its  behavior 
is  like  that  of  a  parasitic  fungus  mycelium,  obtaining  food  from 
the  tissues  through  which  it  grows. 

Tenth.  This  new  feature  of  pollination  and  growth  of  the 
pollen  tube  is  necessitated  because  of  the  more  highly  acquired 
land  habit  of  the  Gymnosperms  and  the  complete  dependence  of 
the  gametophyte  on  the  sporophyte,  while  in  the  Pteridophytes, 
the  gametophytes,  either  from  the  first,  or  as  in  Selaginella,  some 
time  before  fertilization,  becoming  free  from  the  sporophyte  are 
dependent  on  water  as  a  means  of  the  motile  sperms  being  con- 
ducted to  the  archegonia. 

Eleventh.  The  development  of  the  seed,  which  is  a  new  struc- 
ture for  the  propagation  and  spread  of  the  plants.  It  will  be 
recalled  that  Selaginella  almost  reached  the  point  of  forming 
seeds. 


3/4  GENERAL   MORPHOLOGY   OF   PLANTS 

537.  Formula  for  life  history  of  Gymnosperms.*  —  This 
could  be  written  as  follows,  beginning  with  the  sporophyte  or 
second  generation. 


/Microspore  —  Male  Gametophyte      —  sperm  \ 

SpOrOphytC<f    (pollen  grain)         (pollen  grain  tube  and  contents)  J. 

^Macrospore  —  Female 

(beginning  of  (endosper 

endosperm) 

—  Fertilized  egg  —  Sporophyte,  etc.  = 


^Macrospore  —  Female  Gametophyte  —  egg 

(beginning  of  (endosperm  -with  archegonia) 

endosperm) 


_FE_s 
\  ma  sp  —  FG  —  e  / 

If  the  formula  starts  with  the  beginning  of  one  of  the  alternating 
stages  and  represents  the  beginning  and  end  of  each  generation  it 
would  stand  thus,  MC  =  mother  cell  of  spores. 

2nd  Generation  isl  Generation 


FE-  S  -  MC(  . 

\  ma  sp  —  FG  —  e 


Endosperm  and 
Pollen  Grain 

Diagram  No.  VI.  Illustrating  life  cycle  of  a  gymnosperm.  Course  of  deve'opment 
follows  the  direction  indicated  by  the  arrows.  Zygote  equals  fertilized  egg.  Vegetative 
multiplication  by  off  shoots.  Note  the  increase  of  the  sporophyte  and  decrease  of  the  game- 
tophyte. 

*  For  reference. 


CHAPTER  XXXV. 
ANGIOSPERMS.* 

538.  General  characters. — The  Angiosperms  include  the 
members  of  the  second  class  of  seed  plants  (Spermatophytes) . 
They  are  distinguished  from  the  members  of  the  first  class,  the 
Gymnosperms,  chiefly  for  two  reasons.  First,  the  seeds  are 
enclosed  in  a  vessel  or  case.  This  vessel  or  case  is  formed  from 
the  ovary  (an  ovule  case),  sometimes  with  the  cohesion  also  of 
other  parts  of  the  flower  (Chapter  XX) .  Second,  the  presence  of 
the  true  flower,f  usually  with  a  perianth  (see  Chapters  XVI, 
XVII).  The  plants  (which  are  sporophytes)  are  adapted  to  live 
under  a  great  variety  of  conditions  both  in  water  and  on  land. 
There  is  also  a  great  variation  in  size,  from  large  tall  trees  to  the 
shrubs  and  herbs,  some  of  which  are  quite  minute.  The  leaf  is 
typically  a  thin,  expanded  structure,  but  varies  in  plants  living 

To  THE  TEACHER.  The  first  part  of  this  chapter  is  presented  here  as  a 
brief  text  review  of  some  of  the  work  in  Part  I.  The  most  of  the  chapter 
is  too  technical  for  any  but  advanced  students,  and  is  included  here  to  round 
out  the  text  and  sum  up  the  brief  discussions  in  former  chapters  of  develop- 
ment, alternation  of  generations,  life  histories,  etc. 

*  Since  members  of  the  Angiosperms  were  chiefly  used  for  the  study  of 
seeds,  the  different  parts  and  functions  of  the  plant,  this  chapter  will  be 
treated  more  in  the  nature  of  a  brief  review  and  in  pointing  out  the  position 
of  the  different  parts  in  the  life  cycle  when  compared  with  the  other  groups 
of  plants. 

t  The  aggregation  of  sporophylls  along  an  axis  in  the  higher  Pteride- 
phytes  and  in  the  Gymnosperms  is  sometimes  spoken  of  as  a  primitive 
flower.  But  the  "  flower  "  axis  is  elongated,  the  members  are  in  spirals, 
and  there  is  an  absence  of  a  perianth  of  brightly  colored  members.  In  a  few 
of  the  lower  Angiosperms  some  of  the  members  of  the  flowers  are  in  spirals. 
In  the  magnolias  and  tulip  tree  (Liriodendrori)  the  axis  of  the  flower  is  con- 
siderably elongated,  and  it  is  believed  to  represent  a  primitive  condition. 
But  there  is  a  highly  developed  perianth. 

375 


376  GENERAL   MORPHOLOGY   OF   PLANTS 

under  peculiar  conditions  to  stouter  structures,  which  may  be 
quite  large,  or  others  reduced  to  scale-like  bodies.  The  tissues 
are  very  highly  developed,  and  the  presence  of  true  vessels  also 
marks  the  Angiosperms  off  from  most  of  the  Gymnosperms. 


THE    FLOWER. 

539.  The  flower  represents  the  highest  stages  in  evolu- 
tion of  plants. — The  flower  is  the  most  characteristic  feature  of 
the  Angiosperms.  It  was  foreshadowed  in  the  higher  fern  plants 
where  spore-bearing  leaves  (the  sporophylls)  are  massed  together 
at  the  end  of  a  shoot,  forming  a  strobilus.  The  Gymnosperms 
show  an  advance  upon  the  strobilus  of  the  fern  plants,  because 
of  the  development  of  the  ovule,  which  encloses  permanently  the 
macrospore  and  secretes  a  viscous  substance  which  holds  the 
pollen  grain  (microspore)  in  position  where  it  can  germinate,  so 
that  the  sperms  may  be  carried  to  the  egg.  In  addition  to  the 
ovule,  and  the  contrivances  for  enabling  the  sperms  to  reach  the 
egg,  the  flower  of  the  Angiosperms  presents  several  important 
features  which  indicate  an  advance  in  plant  evolution.  These 
may  be  enumerated  as  follows : 

First.  The  appearance  of  a  perianth.— The  development  of 
floral  envelopes  (sepals  and  petals)  which  serve  to  protect  the 
essential  organs  (stamens  and  pistils)  in  the  bud. 

Second.  The  showy  perianth. — The  showy  character  of  the 
floral  envelopes,  because  of  size  and  color,  which  serves  to  attract 
insects  to  aid  in  pollination.  In  some  cases  where  the  flowers 
lack  a  showy  perianth  there  are  colored  bracts  or  leaves  just 
below  the  flower,  or  cluster  of  flowers,  which  serve  the  same  pur- 
pose, as  in  the  flowering  dogwood,  the  dwarf  cornel  or  bunch- 
berry,  the  painted  cup,  etc.  A  striking  example  is  the  PoinseUia 
grown  in  greenhouses  or  conservatories.  This  coloration  of 
bracts  and  leaves  at  the  base  of  the  flower  suggests  how  the 
perianth  may  have  been  developed  from  leaves. 

Third.  Dimorphism,  and  special  adaptation. — Monoecism, 
dicecism,  dichogamy,  and  the  many  peculiarities  in  structure  of 


ANGIOSPERMS  377 

the  members  of  the  flower  which  enforce  cross  pollination  and 
fertilization. 

Fourth.  The  structure  of  the  flower. — The  form  of  the  flower, 
the  number  and  relation  of  its  members  and  relation  of  the  flowers 
in  mass,  which  show  an  advance  from  simple  and  generalized 
flower  types  to  specialized  types  and  specialized  arrangements, 
form  the  basis  for  the  grouping  of  the  Angiosperms  into  classes, 
subclasses,  orders  and  families.  The  more  primitive  flower  types 
probably  possessed  a  large  and  indefinite  number  of  floral  ele- 
ments, which  were  arranged  in  a  spiral  manner  on  the  floral  axis 
following  the  arrangement  of  the  leaves,  since  the  floral  elements 
are  regarded  as  modified  leaves.  Among  the  lowest  of  the  di- 
cotyledons the  buttercup  family  (Ranunculaceae)  illustrates  a 
simple  type  of  flower  structure  and  arrangement.  In  some 
species  there  are  numerous  stamens  and  simple  pistils  in  spirals. 
The  white  water  lilies  show  a  similar  arrangement  of  the  numer- 
ous members  of  the  perianth  and  stamens.  Among  the  higher 
angiosperms  there  is  a  tendency  to  a  definite  and  small  number 
of  plant  elements.  In  the  monocotyledons  this  is  shown  in  the 
trimerous  flowers  (parts  in  three's)  of  so  many  families,  and  in 
the  dicotyledons  by  the  tetramerous  (parts  in  four's)  and  pentam- 
erous  (parts  in  five's)  flowers,  and  by  the  floral  elements  being 
so  crowded  on  the  short  axis  that  they  no  longer  are  in  spirals  but 
in  whorls  or  cycles  (cyclic  arrangement).  This  specialized  con- 
dition, shown  in  the  reduction  from  numerous  parts,  to  a  few 
definite  in  number,  is  regarded  as  showing  a  higher  state  of  evo- 
lution. It  is  often  accompanied  by  the  loss  of  certain  parts  in 
some  flowers,  which  leads  to  two  different  kinds  of  flowers,  on 
the  same  plant  or  on  different  plants,  shown  in  the  ray- flowered 
composites;  also  in  the  difference  in  length  of  the  same  essential 
organs  in  different  flowers  (dichogamy)  or  in  a  difference  in  time 
of  maturity  (proterandry,  proterogeny).  In  the  more  primitive 
flowers  the  parts  are  all  separate,  and  the  flowers  are  actinomor- 
phic  or  radiate  in  the  arrangement  of  the  parts  (radial  symmetry). 
As  the  flower  has  become  more  specialized,  a  change  in  form  to 
bilateral  symmetry  has  taken  place  in  many  groups,  as  in  the 


3/8  GENERAL   MORPHOLOGY   OF  PLANTS 

labiates  (in  mints,  many  legumes,  many  orchids,  etc.),  which 
provides  better  facilities  for  insuring  cross  pollination  by  insects. 
The  fusion  of  parts  of  the  flower  of  different  sets  follows  as  in  epigy- 
nous,  perigynous  or  epipelalous  flowers.  Then  parts  of  the  same 
kind  are  united  by  coalescence  as  in  sympetalous  (petals  united)  and 
synsepalous  (sepals  united)  flowers,  while  syncarpous  fruits  (car- 
pels united  forming  a  compound  pistil)  represent  the  highest  con- 
dition of  the  development  of  the  carpels.  The  massing  of  flowers 
is  also  another  evidence  of  progression.  The  highest  expression 
of  this  arrangement  is  seen  in  the  composite  flowers  where  nu- 
merous small  flowers  unite  to  form  "  heads."  In  many  of  these, 
the  outer  circle  of  flowers  is  conspicuous  by  the  lateral  elongation 
of  the  corolla  tube,  which  is  bright  colored  and  serves  to  attract 
insects  to  the  head  where  there  are  many  proterandrous  flowers 
insuring  cross  pollination.  It  is  to  be  noted  also  that  the  com- 
posites have  reached  the  highest  stage  of  the  union  of  parts,  and 
they  are  recognized  as  the  highest  expression  of  the  development 
of  the  flower. 

Fifth.  The  closed  seed  case. — The  formation  of  a  closed 
capsule  or  case  (ovary)  containing  the  ovule,  which  is  an  advance 
over  the  open  seed  carpel  in  the  Gymnosperms. 

540.  The  parts  of  the  flower  are  modified  leaves.— The 
sepals  and  petals  are  leaf-like  in  form.  They  are  leaves  which  have 
become  modified  in  their  development  to  serve  certain  definite 
useful  purposes  for  the  plant,  as  protecting  envelopes  while  the 
essential  parts  of  the  flower  are  forming,  and  the  petals  often 
serve  to  attract  insects  which  aid  in  cross  pollination.  In  some 
flowers  the  sepals  are  green  in  color,  or  the  same  form  as  the 
leaves  and  arranged  in  the  same  way  on  the  stem,  as  in  the  wake 
robin  (  Trillium) .  In  this  same  plant  the  petals  sometimes  take 
on  a  green  color,  and  thus  more  clearly  show  that  as  members  of 
the  plant  body  they  are  leaves  (floral  leaves).  This  transfor- 
mation of  the  sepals  and  petals  to  leaves  also  occurs  now  and  then 
in  many  other  plants.  The  stamens  and  pistils  (carpels  rather) 
are  also  modified  leaves.  Their  leaf  nature  is  sometimes  mani- 
fest, under  peculiar  conditions,  when  the  stamens  and  pistils 
. 


ANGIOSPERMS  3/9 

expand  into  green  leaves  showing  also  some  intermediate  stages 
with  partly  developed  anther  sacs  or  ovules  on  them. 

541.  The  stamen  is  a  microsporophyll. — The  function  of 
the  stamen  is  the  production  of  pollen.     Each  pollen  grain  is 
a  spore,  and  four  are  formed  from  a  mother  cell  in  the  anther 
sac  just  as  the  spores  of  the  ferns,  mosses  and  liverworts  are 
formed.     When  the  pollen  grain  germinates  it  produces  the  pollen 
tube  and  two  sperm  cells.     It  is  therefore  the  male  gametophyte. 
The  pollen  spore  is  the  microspore,  the  anther  sac  is  the  micro- 
sporangium,  and  the  stamen  is  the  microsporophyll. 

542.  The  pistil,  or  carpel,  is  a  macrosporophyll  (=mega- 
sporophyll). — The  simple  pistil  is  a  carpel,  while  a  compound 
pistil  is  formed  of  several  carpels  united.     The  pistil  is  com- 
posed of  the  ovary,  the  style  (which  may  be  wanting)  and  the 
stigma.     The  function  of  the  ovary  is  the  production  of  ovules 
with  the  contained  embryo  sac  and  egg.     The  egg  it  will  be 
remembered  in  the  Gymnosperms  is  developed  by  the  game- 
tophyte.    The  embryo  sac  with  the  egg  is  the  female  gametophyte 
of  the  Angiosperms.     It  represents  the  macrospore,  just  as  the 
female  prothallium  in  Selaginella  enclosed  by  the  spore  wall  is 
the  macrospore  (or  megaspore). 

The  ovule  then  which  produces  the  macrospore  is  the  macro- 
sporangium,  and  the  carpel  is  the  macrosporophyll. 

543.  The  sexual  organs  of  Angiosperms.— The  stamens  and 
pistils  are  often  spoken  of  as  the  sexual  organs  of  the  flower. 
This  is  not  strictly  correct,  for  the  sexual  organs  are  borne  on  the 
gametophyte  and  are  a  part  of  it,  while  the  stamen  and  pistil 
are  parts  of  the  s^rophyte.     While  it  is  not  strictly  correct  then 
to  say  that  the  stamen  is  a  sexual  organ,  or  male  organ,  it  is  a 
male  member  of  the  flower  for  it  is  a  flower  member.     We  should 
then  distinguish  between  its  functions  as  organ  and  member.     It 
is  an  organ  when  we  consider  pollen  production,  but  it  is  not  a 
sexual  organ,  for  the  pollen  sac  is  not  a  sperm  case  (antheridium) , 
it  is  a  spore  case.    The  spore  case  is  a  part  of  the  sporophyll 
(stamen).     But  when  we  consider  fertilization,  the  sperms  are 
formed  in  the  sperm  case  (antheridium)   which  is  here  much 


380  GENERAL   MORPHOLOGY   OF  PLANTS 

reduced,  consisting  of  the  tube  cell  and  generative  cell  (central 
cell),  i.e.,  the  mature  pollen  grain.  The  stamen  is  a  member  of 
the  flower  when  we  are  considering  the  principal  parts  of  the 
flower  structure  or  form.  It  possesses  certain  characters  of 
form,  size,  structure,  etc.,  which  are  correlated  with  its  functions 
of  spore  production,  and  since  the  spore  on  germination  produces 
the  male  sexual  organs,  these  characters  possessed  by  the  stamen 
are  qualities  of  maleness.  From  this  point  of  view  the  stamen  is 
a  male  member  of  the  flower.  In  a  similar  way  the  pistil  is  nat 
the  female  sexual  organ.  It  is  the  female  member  of  the  flower 
and  is  the  organ  for  the  production  of  the  macrospore  (or  female 
prothallium)  which  in  turn  gives  rise  to  the  sexual  organ,  here 
reduced  to  the  egg,  the  wall  of  its  case  wanting. 

The  following  table  will  serve  to  indicate  these  relations. 

Stamen  =  spore-bearing  leaf  =  male  member  of  flower. 

Anther  locule       =  sporangium. 

Pollen  grain         =  small     spore  =  reduced     male     prothallium 

and  sexual  organ,  sterile  part  of  prothallium 

not  formed. 

Pistil,  or  carpel  =  spore-bearing  leaf  =  female  member  of  flower. 
Ovule  =  sporangium. 

Embryo  sac         =  large  spore  =  female  prothallium   containing 

the  egg. 
The  egg  =  a  reduced  archegonium  =  the  female  sexual 

organ. 

544.  Life  history  of  the  Angiosperms. — Since  a  thorough 
study  has  been  made  of  the  sporophyte  of  the  Angiosperms  in 
Part  I,  this  account  will  treat  briefly  of  the  gametophytes  and  the 
early  stage  of  the  embryo,  in  order  to  form  a  basis  for  comparison 
with  the  lower  plants. 

545.  The  male  gametophyte. — The  male  gametophyte  be- 
gins with  the    pollen  grain,  or   microspore,  four  of  which   are 
formed  from  a  mother  cell  in  the  anther  sac.     When  the  pollen 
grain  is  ripe  it  usually  consists  of  two  cells,  one  the  tube  cell  with 
a  prominent  nucleus,  the  other  a  smaller  cell  with  no  cell  wall, 


ANGIOSPERMS 


381 


Fig.  375- 
Nearly      mature 


which  floats  in  the  tube  cell  but  at  first  is  separated  by  a  thin 
arched  cell  wall  (fig.  375).  This  is  the  generative  cell  or  body 
cell,  and  was  formed  on  germination  of  the  young 
microspore  by  the  division  of  the  single  nucleus  of 
the  microspore  before  the  pollen  grain  was  ripe. 
After  the  pollen  grain  has  reached  the  stigma  of 
the  pistil  (see  Pollination,  Chapter  XVIII)  it  germi- 
nates, producing  a  tube  which  travels  down  the 
pollen  sj^^jjj-  styje  (or  m  fae  stylar  canal  in  some  plants) ,  enters 
five  cen he  genera"  the  ovary,  and  passing  through  the  micropyle  * 
bores  its  way  through  the  nucellus  until  it  reaches 
the  embryo  sac.  The  tube  nucleus  has  followed  along  with  the 
advance  of  the  tube.  Soon  after  the  pollen  grain  germinates  the 
generative  cell  divides  into  two  cells,  the  sperm  cells,  and  these 
move  into  the  tube,  if  the  generative  cell  was  not  already  there 
before  division.  The  stigma  of  the  pistil  is  covered  by  a  moist 
somewhat  viscous  secretion  which  holds  the  pollen  grains.  The 
moisture  and  certain  saccharine  or  other  secretions  favor  or 
stimulate  the  germination  of  the  pollen  grain. 

546.  The  female  gametophyte. — The  female  gametophyte 
is  developed  from  a  special  cell  in  the  nucellus  of  the  ovule, 
The  ovule  is  an  outgrowth  usually 
from  some  part  of  the  ovary  and 
enclosed  by  it  (the  main  part  of 
the  carpel  or  macrosporophyll  which 
in  development  folds  in  such  a  way 
as  to  form  a  case).  It  is  the 
macrosporangium  (or  megasporan- 
gium).  It  consists  of  the  nucellus 
surrounded  by  two  coats  which 
do  not  quite  cover  up  the  nucellus  SA  $ 
•at  one  end,  thus  leaving  a  minute  3S&2 
opening  (the  micropyle).  In  the  pollen  grain' 
lily  a  subepidermal  cell  in  the  nucellus,  near  the  micro- 
pyle, becomes  larger  than  its  neighbors,  with  a  large  nu- 

*  In  a  few  plants,  as  in  some  of  the  ament-bearing  plants,  the  pollen  tube 
enters  the  ovule  at  the  chalaza  end. 


G  erminating  spores 
(pr>llen  grains)  of  pel- 
t.mdra;  generative  nu- 
cleus in  on- undivided, 


382 


GENERAL   MORPHOLOGY   OF   PLANTS 


cleus  and  abundant  protoplasm.  This  cell  continues  to  en- 
large until  it  forms  a  large  usually  elongated  sac,  the  embryo  sac. 
During  its  enlargement  the  nucleus  divides  by  three  successive 
divisions  into  ei^ht  nuclei  which  have  a  definite  arrangement  in 


I'ig.  377- 

Podophyllum  peltatum,  ovule  containing  mature  embryo  sac;  two  synergids,  and  eggs  at  left, 
endosperm  nucleus  in  center,  three  antipodal  cells  at  right. 

the  embryo  sac.  At  first  there  are  four  nuclei  at  the  outer  end 
(next  the  micropyle,  called  the  micropylar  end  of  embryo  sac) ,  and 

four  at  the  base  (called  the  antip- 
odal end).  But  soon  one  nucleus 
from  each  pole  (called  polar  nu- 
clei) of  the  embryo  sac  moves  to 
the  center,  where  they  fuse  to  form 
the  primary  endosperm  nucleus 
of  the  endosperm.  This  leaves 
three  nuclei  in  each  end  of  the 
embryo  sac.  The  three  at  the 
base  are  called  antipodals.  They 
Fl?;  j78'  usually  soon  degenerate.  The 

Macrospore  (one-celled  stage)  of  Lihum.  * 

three  at  the    micropylar  end  are 

called  together  the  egg  apparatus.  The  two  nearest  the  micro- 
pylar end  are  called  the  synergids,  which  means  helpers  or  co- 
workers,  because  it  was  once  thought  they  assisted  the  pollen 


ANGIOSPERMS 


383 


tube  in  bringing  the  sperm  cell  to  the  egg.     The  third  nucleus  of 
the  egg  apparatus  is  that  of  the  egg  cell. 

547.  Fertilization. — When  the  pollen  tube  has  reached  the 
embryo  sac  it  opens  at  the  end,  and  the  sperm  cells  with  some  of 
the  protoplasm  are  emptied.  One  of  the  sperm  nuclei  unites 
with  the  egg  nucleus  bringing  about  fertilization.  The  second 


Fig.  379- 

Two-  and  four-celled  stage  of  embryo  sac  of  Lilium.      The  middle  one 
shows  division  of  nuclei  to  form  the  four-celled  stage.     (Easter  lily.) 

sperm,  in  a  number  of  plants,  has  been  found  to  join  the  two 
polar  nuclei  in  the  center  of  the  embryo  sac,  the  three  nuclei 
fusing  to  form  the  primary  endosperm  nucleus.  This  is  called 
double  fertilization, 

548.  The  endosperm  of  the  Angiosperms.— The  primary 
endosperm  nucleus,  formed  by  the  fusion  of  the  two  polar  nuclei 
(and  sometimes  by  triple  fusion  with  the  second  sperm  nucleus), 
develops  the  endosperm.  The  nucleus  divides  successively  into 
a  large  number  of  free  nuclei  arranged  in  the  protoplasm,  which 


384 


GENERAL   MORPHOLOGY   OF  PLANTS 


form  a  peripheral  layer  in  the  embryo  sac  and  are  later  sepa- 
rated by  cell  walls,  thus  forming  the  cellular  endosperm.  This 
serves  as  food  for  the  embryo  just  as  in  the  case  of  the  Gymno- 
sperms,  but  its  origin  is  different.  In  the  formation  of  the 


Hg-  380.  Fig.  381. 

Mature  embryo  sac  (young  pro-        Diagrammatic  section  of  ovary  and  ovule  at  time  of  fer- 

thallium)  of  Lilium.  »/,  micropylar    tilization  in  angiosperm.     /.  funicle  of  ovule;  n,  nucellus; 

end;    5,    synergids;   £,   egg;   Pn,    m,  micropyle;  b,  antipodal  cells  of  embryo  sac;  e,  endo- 

polar     nuclei;     Ant,    antipodals.    sperm  nucleus;  k,  egg  cell  and  synergids;  ai,  outer  integ- 

(Easter  lily.)  ument  of  ovule ;  «',  inner  integument.    The  track  of  the 

pollen  tube  is   shown  down  through  the   style,  walls  of 

the  ovary  to  the  micropylar  end  of  the  embryo  sac. 

endosperm  the  tissue  of  the  nucellus  (inner  portion  of  the  macro- 
sporangium)  is  usually  all  consumed,  leaving  only  a  thin,  dead 
outer  portion  surrounded  by  the  ovule  coats,  or  integuments.  In 
a  few  plants,  however  (water  lily  family,  pepper  family,  etc.), 
much  of  the  nucellus  remains  in  the  seed  as  a  nutritive  tissue 


ANGIOSPERMS 


385 


for  the  seedling  at  time  of  germination.  This  is  called  the  peri- 
sperm.  The  endosperm  of  the  Angiosperms  is  not  developed 
unless  fertilization  takes  place,  even  in  those  cases  where  double 
fertilization  may  not  occur. 

549.  In  case  of  crosses  between  different  varieties  of  plants,  the 
effect  of  the  cross  usually  is  not  apparent  in  the  seed  because  the 
qualities  of  the  two  parents  are  united  in  the  embryo  and  would 
not  be  shown  until  the  embryo  develops  into  a  plant,  or  in  a  fol- 
lowing generation.  Sometimes,  however,  the  effect  of  the  cross 
is  seen  in  the  seed  formed  following  fertilization,  as  for  example 


Fig.  382. 

Seed  of  violet,  external  view,  and 
section.  The  section  shows  the  embryo 
lying  in  the  endosperm. 


Fig.  383- 

Section  of  fruit  of  pepper  (Piper 
nigrum),  showing  small  embryo  lying 
in  a  small  quantity  of  whitish  endo- 
sperm at  one  end,  the  perisperm 
occupying  the  larger  part  of  the  in- 
terior, surrounded  by  pericarp. 


In  corn,  where  there  is  a  change  in  color  of  the  seed  when  differ- 
ent colored  varieties  are  crossed.  This  phenomenon  is  called 
xenia  and  is  perhaps  the  result  of  double  fertilization,  the  fusion 
of  the  second  sperm  nucleus  with  the  two  polar  nuclei  to  form 
the  primary  endosperm  nucleus  which  forms  a  hybrid  endosperm. 
550.  The  embryo  and  seed.— The  fertilized  egg  cell  which  is 
near  the  micropylar  end  of  the  embryo  sac,  now  by  a  series  of 
divisions,  and  by  growth,  forms  the  embryo.  At  first  it  forms  a 
simple  cell  mass  with  a  suspensor  at  one  end,  which  pushes  the 
growing  point  down  into  the  mass  of  endosperm.  Soon  the  parts 
of  the  embryo  (root,  stem  and  leaf  bud)  are  organized  and  the 
seed  ripens.  In  some  plants  only  a  small  part  of  the  endosperm 
is  used  by  the  embryo  before  the  seed  ripens,,  as  in  the  corn,  cereals, 
etc.  (albuminous  seeds) ;  in  others  the  endosperm  is  all  consumed 


386 


GENERAL   MORPHOLOGY   OF   PLANTS 


Ripened  ovule.  •( 


by  the  forming  embryo,  and  is  stored  in  the  cotyledons,  as  in  the 
bean,  pea,  oak  (exalbuminous  seeds),  and  the  remnant  of  the 
endosperm  forms  a  thin  papery  membrane  around  the  embry,  . 
All  of  these  changes  take  place  within  the  ovule  while  it  is  still  at- 
tached to  the  ovary  and  nourished  by  the  sporophyte.  The  seed 
at  maturity  then  consists  of  the  embryo,  surrounded  by  the  endo- 
sperm or  its  remnants,  and  the  seed  coats  which  are  formed  from 
the  coats,  or  integuments,  of  the  ovule.  In  some  seeds  there  is 
in  addition  the  perisperm  (see  paragraph  548) . 

551.  Synopsis  of  the  seed. — The  following  table  will  show 
those  parts  composing  the  seed. 

Aril,  rarely  present.* 

Ovular  coats   (one  or  two   usually  present), 

the  testa. 

Funicle  (stalk  of  ovule),  raphe  (portion  of 
funicle  when  bent  on  to  the  side  of  ovule), 
micropyle,  hilum  (scar  where  seed  was 
attached  to  ovary). 

Remnant   of    the    nucellus    (central    part    of 
ovule);    sometimes   nucellus    remains   as 
Perisperm  in  some  albuminous  seeds. 
Endosperm,  present  in  albuminous  seeds. 

Embryo  within  surrounded  by  endosperm  when  this  is  present, 
or  by  the  remnant  of  nucellus,  and  by  the  ovular    coats 
which   make  the  testa      In  many  seeds  (example,  bean) 
,          the    endosperm   is   transferred    to    the    cotyledons   which 
become  fleshy   (exalbuminous  seeds). 

COMPARATIVE  REVIEW   OF  THE  ANGIOSPERMS. 

552.  Origin  of  the  Angiosperms. — Botanists  are  not  agreed 
as  to  the  origin  of  the  Angiosperms,  nor  as  to  whether  the  mono- 
cotyledons or  dicotyledons  were  the  lowest  group.     Some  have 
suggested  that  the  Angiosperms  were  derived  from  'a  Gymno- 
sperm-like  ancestor  similar  to  Ginkgo,  while  others  believe  they 
were  perhaps  derived  from  early  plants  similar  to  some  of  the 

*  The  aril  is  present  in  ginkgo  and  the  yew,  as  a  collar  at  the  base  of  the 
ovule  which  in  the  yew  grows  to  form  the  red  fleshy  covering  of  the  berry. 
In  the  milkweed  and  willow  there  is  a  hairy  aril. 


The  seed. 


ANGIOSPERMS  387 

higher  fern  plants  (related  to  Selaginella,  etc.).  The  two  classes 
of  seed  plants,  the  Gymnosperms  and  Angiosperms,  probably 
represent  di  rergent  lines  of  development  from  the  same  or  related 
stock  belonging  to  the  Pteridophytes  of  geologic  times,  that  is  of 
a  very  early  past,  for  there  are  fossil  remains  of  both  at  a  very 
early  period.  Some  of  the  characters  possessed  by  the  Angio- 
sperms which  mark  an  advance  over  those  of  the  fern  plants  are 
possessed  by  the  Gymnosperms  also.  Taking  the  Angiosperms 
alone  (see  paragraph  536  for  advances  in  the  Gymnosperms)  the 
principal  advances  may  be  enumerated  as  follows: 

First.  The  more  highly  developed  tissue  systems  in  the  parts  of 
the  plant  body,  root,  stem  and  leaf,  with  a  more  efficient  con- 
ducting system  with  true  vessels. 

Second.  The  development  of  the  parts  from  a  growing  point, 
or  meristem,  consisting  of  a  group  of  cells,  instead  of  from  a 
single  apical  cell. 

Third.  The  collateral  arrangement  of  the  tissues  in  the  vascu- 
lar bundles;  in  the  dicotyledons  the  cyclic  arrangement  of  open 
bundles  which  permits  of  .indefinite  growth  of  the  stem  resulting 
in  massive  trunks  (also  a  character  of  many  of  the  Gymnosperms) . 
In  the  monocotyledons  the  bundles  are  scattered  in  the  funda- 
mental tissue  of  the  stem,  which  soon  pass  over  into  permanent 
tissue  and  the  development  of  massive  tree  trunks  is  limited. 

Fourth.  The  great  variety  of  vegetative  forms,  trees,  shrubs 
and  herbs,  with  their  adaptation  to  an  aquatic  as  well  as  a  land 
habit,  and,  especially  in  the  latter,  the  adaptation  to  a  great  variety 
of  climate  and  soil  fits  them  for  growing  in  climates  from  the 
tropic  to  the  subtropic  regions,  in  swamps,  deserts,  plains  and 
steppes,  as  well  as  in  regions  more  temperate  as  regards  climate 
and  moisture  content  of  the  soil.  Many  are  adapted  also  to 
grow  as  shade  plants  or  climbers.  With  this  great  variety  of 
habit  and  character  the  Angiosperms  are  especially  fitted  to 
compete  successfully  with  climate,  soil,  and  with  other  groups  of 
plants. 

Fifth.  The  absolute  prevalence  of  heterospory  which  insures 
cross  fertilization  as  far  as  the  gametophytes  are  concerned,  but 


388  GENERAL   MORPHOLOGY   OF   PLANTS 


re- 


is  not  necessarily  cross  fertilization  so  far  as  the  plants  (sporo- 
phytes)  are  concerned. 

Sixth.  In  the  retention  of  the  macrospore  in  the  ovule  (macro- 
sporangium)  ,  and  the  development  of  an  embryo  plant,  while  still 
attached  to  and  nourished  by  the  old  sporophyte,  the  seed  is  pro- 
duced with  its  protecting  coats  and  stored  food,  which  more  cer- 
tainly provides  for  the  distribution  and  perpetuation  of  the  species 
under  a  great  variety  of  adverse  conditions. 

Seventh.  The  increasing  importance  and  greater  complexity  of 
the  sporophyte  in  the  liverworts,  mosses,  fern  plants  and  Gymno- 
sperms  have  been  accompanied  by  a  gradual  diminution  and 
degeneration  of  the  gametophyte,  and  in  the  Angiosperms  this 
degeneration  of  the  gametophyte  phase  has  gone  still  farther, 
which  is  another  evidence  of  the  higher  evolution  of  the  Angio- 
sperms. The  male  gametophyte  *  consists  of  two  cells,  a  tube 
cell  with  a  cell  wall  enclosing  a  central  cell  or  generative  cell 
(pollen  grain  or  microspore)  which  lacks  a  cell  wall  and  floats  in 
the  protoplasm  of  the  cell,  and  forms  two  sperm  cells  on  division, 
the  tube  cell  growing  as  a  parasite  through  the  stigma  and  stye  to 
the  ovule.  In  some  of  the  Gymnosperms  the  male  gametophyte 
is  just  as  simple  (the  yew,  Taxus,  for  example).  The  female 
gametophyte  shows  a  greater  degeneration  even  than  in  the 
Gymnosperms,  being  in  the  Angiosperms  reduced  to  a  few  nuclei 
in  cytoplasm  not  separated  by  cell  walls  (the  embryo  sac) ,  and  the 
archegonium  is  reduced  to  the  egg  cell.  Sometimes  the  female 
gametophyte  is  developed  from  what  may  ba  considered  a  true 
spore,  and  in  other  plants  from  the  mother  cell  direct,  thus  still 
farther  cutting  short  the  development  of  the  gametophyte  gen- 
eration. 

Eighth.    The    development    of    the    flower,   which   marks    the 

*  The  male  gametophyte  probably  represents  solely  a  reduced  anthe- 
ridium,  or  sexual  organ.  The  tube  cell  may  be  the  wall  of  the  antheridium 
here  reduced  to  a  single  cell,  for  in  Selaginella  and  Isoetes  the  antheridium 
is  formed  from  the  larger  part  of  the  microspore,  though  wall  cells  com- 
pletely surround  the  central  cell  which  forms  the  sperms.  However,  in  some 
of  the  heterosporous  ferns  (the  water  fern  Salmnia)  the  antheridium  does  not 
have  a  complete  wall  of  cells  surrounding  the  central  cell. 


ANGIOSPERMS  389 

climax  in  the  evolution  of  the  known  plants  and  was  fore- 
shadowed in  the  massing  of  the  sporophylls  of  the  higher  Pterido- 
phytes. 

The  most  striking  advances  shown  in  the  flower  are  as 
follows : 

1.  The  evolution  of  floral    envelopes  for   protection    and  for 
attracting  insects  to  aid  in  cross  pollination. 

2.  The  change  from  radial  symmetry  to  bilateral  symmetry  in 
certain  flowers. 

3.  The  progression  from  indefinite  and  numerous  flower  parts 
to  a  definite  and  limited  number. 

4.  The  change  from  free  parts  of  hypogynous  flowers  to  union 
of  parts  as  shown  in  perigynous,  epigynous,  epipetalous,   sym- 
petalous and   synsepalous   flowers,   reaching   the   climax   in    the 
composites. 

5.  Dimorphism  or  flowers  and  flower  parts  shown  in  monaecism, 
di'tcism,  dichogamy,  requiring  cross  fertilization. 

6.  Proterandry  and  proten>gyny,  also  requiring  cross  fertiliza- 
tion. 

Ninth.  The  development  of  the  ovule  case,  or  seed  case,  which 
when  young  is  a  small  and  open  carpel  with  exposed  ovules,  but 
later  infolds,  thus  enclosing  the  ovules  which  become  seeds. 

Tenth.  The  seed,  consisting  of  the  ovule  with  its  coats  which 
become  the  seed  coats  containing  the  embryo,  and  food  sub- 
stances. 

553.  Formula  for  life  history  of  the  Angiosperms.* — This 
would  be  similar  to  that  of  the  Gymnosperms  and  may  be  written 
as  follows: 

/Microspore  —  Male  Gametophyte    —  sperm. 

(pollen  grain)  (pollen  tube  and  contents)  \ —  - 

Macrospore  —  Female  Gametophyte  —  egg     / 

(embryo  sac)  (embryo  sac  and  contents) 

Fertilized  egg  —  Sporophyte,  etc.     In  abbreviated  form  this  be- 
comes S  /  mi  Sp  ~  "  S  )FE  —  S.,  etc.     Starting  with  the 
N  ma  sp  —  FG  —  e  / 

*  For  reference  only. 


390  GENERAL   MORPHOLOGY   OF  PLANTS 

gametophyte  or  first  generation,  and  reducing  the  two  kinds 
of  prothallia  to  one,  the  formula  becomes  G  '  ^  FE  —  S  —  asp 

—  G.,  etc.,  which  represents  the  alternation  of  generations, 
and  compared  with  that  of  the  ferns  and  mosses  is  seen  to  be 
identical. 


ANGIOSPERMS 


39' 


CHAPTER   XXXVI. 

ECONOMIC    OR    USEFUL    PLANTS.* 

MONOCOTYLEDONES. 

554.  The  grass  family  (Gramineae).  The  most  useful  mem- 
bers of  the  grass  family  are  the  grasses,  the  cereals  (or  grains) , 
wheat,  oats,  barley,  rye,  maize,  and  rice,  the  canes  and  bamboo. 
The  members  of  the  family  have  a  very  wide  distribution  over 
the  earth,  some  growing  in  the  wild  state  while  most  of  the  use- 
ful ones  are  kept  under  cultivation.  While  they  display  a  great 
variety  in  individual  appearance,  the  flower  structure  is  very 
similar  in  all,  and  is  very  simple  (see  Chapter  XVII  for  the 
flower  of  maize  and  oats).  The  true  grasses,  i.e.,  the  members 
of  the  grass  family,  which  are  popularly  called  grasses,  include  a 
considerable  variety  of  cultivated  forms,  which  are  often  grown 
for  special  purposes  because  of  their  fitness  for  special  conditions, 

*  To  THE  TEACHER.  Only  the  larger  and  more  important  families  are 
intended  for  study.  The  others  are  included  simply  to  round  out  the  topic 
as  a  whole.  Many  of  the  economic  plants  will  be  studied  in  connection  with 
the  study  of  seedlings,  the  parts  of  the  full-grown  plant,  the  studies  of  flowers, 
fruit  and  seed  in  the  early  part  of  the  course.  This  chapter  is  prepared  for 
the  purpose  of  discussing  some  of  the  principal  useful  plants,  with  notes  on 
their  history,  distribution,  etc.,  and  at  the  same  time  for  the  purpose  of  show- 
ing their  relationship  in  the  system  of  classification  among  seed  plants,  and 
some  of  our  common  wild  flowers  which  are  their  relatives  and  belong  to  the 
same  family.  The  teacher  can  arrange  for  discussions,  readings,  and  exhi- 
bitions of  various  topics  as  material  and  time  will  permit.  Doubtless  in 
many  cases  very  little  or  no  time  can  be  given  to  the  matter  of  the  chapter  in 
the  regular  work,  but  it  will  serve  a  good  purpose  for  reference.  A  per- 
manent collection  of  the  more  important  economic  plants  including  fruits, 
nuts,  woods,  plant  products,  etc.,  would  be  a  valuable  possession  for  the 
schools. 

392 


ECONOMIC   OR    USEFUL   PLANTS  393 

as  lawn  grasses,  for  pasture  and  for  hay.  The  red  top  is  often 
grown  for  pasture,  while  timothy  is  widely  grown  for  hay,  and 
the  Kentucky  blue  grass  or  June  grass  is  valuable  for  lawns  as 
well  as  for  pasture  and  hay. 

555.  The   cereals,  or   grains. — The   cereals,  or  grains,  are 
grasses  which  are  cultivated  chiefly  for  the  food  present  in  the 
seed  fruit  or  grain,  though  the  straw  often  makes  excellent  fodder 
for  stock  and  is  used  for  a  variety  of  other  purposes.     The  chief 
cereals  are  wheat,  rye,  oats,  barley,  rice,  corn  or  maize. 

556.  Wheat. — Wheat  is  believed  to  have  originated  from  a 
species  (Triticum  ovatum)  native  to   the    Mediterranean  region. 


Fig.  384- 

Bearded  and  bald  wheat  heads  (common  varieties  of  wheats  grown  at  Pullman, 
Washington).     From  Bureau  of  Plant  Industry. 

It  is  one  of  the  staple  crops  of  the  north  temperate  regions,  since 
wheat  requires  cool  weather  for  the  early  stages  of  growth  to 
cause  it  to  stool  and  become  stocky  and  vigorous.  A  great  many 
different  varieties  of  wheat  are  propagated  for  the  different  grades 
of  flour,  because  of  their  relation  to  different  kinds  of  soil  or 
climate.  The  grains  vary  as  to  color  and  hardness.  The  heads 
vary  as  to  bearded  or  bald  varieties,  the  awns  on  the  palets  being 
very  long  and  barbed  in  the  bearded  wheat.  All  of  these  kinds 


394  GENERAL    MORPHOLOGY    OF   PLANTS 

are  usually  classed  under  two  heads,  as  winter  wheat  and  spring 
wheat.  Winter  wheat  is  sown  in  late  summer  or  early  autumn. 
The  cool  weather  of  autumn  checks  the  rapid  growth  and  causes 
it  to  "  stool,"  i.e.,  to  throw  out  numerous  branches  or  "  suckers," 
while  the  stalks  do  not  become  tall.  It  is  very  hardy  in  the 
young  stages  and  withstands  the  cold  winter,  though  open  win- 
ters with  alternate  thawing  and  freezing  often  cause  it  to 
"  heave,"  so  that  it  dies  because  the  roots  are  lifted  out  of  the 
ground.  The  spring  wheats  are  sown  in  early  spring,  but  they  do 
well  only  in  the  extreme  northern  latitudes  of  the  temperate 
region.  When  grown  in  the  middle  temperate  regions  spring 
wheat  is  an  uncertain  crop,  and  it  is  necessary  to  obtain  seed 
from  wheat  grown  in  northern  latitudes  to  obtain  the  best  results. 
For  example,  much  of  the  seed  spring  wheat  for  the  !  Northern 
States  is  grown  in  Canada.  When  spring  wheat  can  be  sown 
early  and  the  spring  season  is  cold,  an  opportunity  is  given  for 
the  plants  to  stool  and  make  a  vigorous  and  stocky  growth.  While 
wheat  is  grown  successfully  throughout  the  Northern  States  and 
Canada,  the  great  wheat  section  is  in  some  of  the  Northwestern 
States  and  in  Manitoba,  though  as  high  yields  per  acre  are 
obtained  in  New  York  as  in  the  great  wheat-growing  sections. 
The  annual  production  in  the  United  States  amounts  to  from 
$300,000,000  to  $500,000,000. 

The  "  hard  "  wheats,  i.e.,  those  with  a  hard  grain,  have  a 
greater  nitrogen  content  than  the  "  soft  "  or  starchy  wheats,  and 
thus  are  more  nutritious.  The  hard  wheats  are  better  for  mak- 
ing bread,  rolls,  etc.,  because  the  "  dough  "  rises  better  than  that 
made  from  the  soft  wheats.  The  soft  wheats  are  better  for  cakes 
and  for  pastry.  Millers,  however,  often  mix  soft  wheat  with  the 
hard  because  the  latter  is  more  expensive.  The  spring  wheats 
grown  in  Canada,  Minnesota,  Dakota,  and  other  places  in  the 
northwest,  where  there  is  a  low  rainfall  and  consequently  drier 
climate,  are  chiefly  hard  wheats,  and  yield  the  best  flour.  In 
some  sections  winter  wheat  is  not  grown,  or  is  grown  to  a  much 
less  extent  because  of  the  severe  winters  with  little  snow  and 
high  wind.  Some  winter  wheats  are,  however,  hard  wheats; 


ECONOMIC   OR    USEFUL   PLANTS 


395 


examples,  those  grown  in  Kansas  and  the  southwest.  These 
however  are  not  quite  equal  to  the  spring  wheat  of  the  north- 
west; because  of  the  somewhat  more  extended  period  of  growth, 
there  is  a  larger  proportion  of  starch. 

557.  Rye. — (Secale  cereale,  believed  to  be  native  in  the  region 
between  the  Black  and  Caspian  Seas).  —  This  cereal  resembles 
wheat,  but  the  heads 


are  longer  and  more 
slender,  the  grainsbe- 
ing  more  slender,  and 
the  straw  is  stiff  and 
long.  It  is  very  ex- 
tensively cultivated 
in  northern  Europe, 
and  is  there  more 
commonly  used  for 
bread  than  in  this 
country  where  the 
crop  is  small.  Russia 
is  the  greatest  rye- 
growing  country  in 
the  world.  Winter 
varieties  are  most 
generally  used,  and 
are  sown  in  the  au- 
tumn. Rye  does  well 
on  much  poorer  soil 
than  wheat,  and  the 
crop  is  sometimes 
used  for  green  soiling 
by  plowing  it  under  to  enrich  the  soil.  Besides  its  use  for  food 
rye  is  used  in  making  some  of  the  grades  of  whisky. 

558.  Oats. — The  flowers  of  oats  (Avena  saliva)  are.  in  loose 
panicles  and  the  grains  are  permanently  covered  by  the  palets, 
not  shelling  out  as  in  wheat.  In  northern  climates  they  are  sown 
early  in  the  spring  to  secure  the  stocky  growth.  In  southern 


Fig.  385. 

Oat  heads,  showing  the  common  branching  one  and  a  side 
head  variety  (flag  oats).     From  Bureau  Plant  Industry. 


39^ 


GENERAL   MORPHOLOGY   OF   PLANTS 


latitudes  they  are  often  sown  in  the  autumn,  since  tne  winters 
are  rarely  severe  enough  to  kill  the  young  plants.  Oats  are 
grown  chiefly  for  stock  feeding,  but  oatmeal  for  household  use  is 
obtained  by  special  processes  for  removing  the  closely  adhering 
palets. 

559.   Barley. — Barley  resembles   wheat   in   the  form   of   the 
fruiting  heads,  but  is  like  oats  in  the  grain  being  permanently  and 

closely  covered  by  the  palets. 
It  is  grown  from  arctic  to 
tropical  regions,  being  accli- 
mated over  a  greater  region 
than  other  cereals.  Barley  is 
chiefly  used  for  making  malt 
in  breweries,  though  both  the 
grain  and  straw  are  used  as 
food  for  stock.  It  is  also  used 
for  making  certain  of  the  fine 
grades  of  whisky,  as  Scotch 
whisky.  Spring  or  summer 
barley  is  a  four-rowed  species 
(Hordeumvulgare),  while  win- 
ter barley  (H .  hexaslichon)  is 
six-rowed  and  earlier  intro- 
duced into  cultivation. 

560.  Rice. —  This  cereal 
(Oryza  saliva)  is  grown  chiefly 
in  China,  Japan,  India,  and  the 

From  Bureau  Plant  Industry. 

have  been  its  home.  It  is  extensively  cultivated  in  this  country  in 
South  Carolina,  which  produces  the  best  rice  in  the  world,  and 
in  Louisiana.  The  industry  is  being  developed  in  other  South 
Atlantic  Gulf  States.  It  requires  a  rich  moist  soil,  which  can  be 
flooded  at  certain  seasons,  though  varieties  are  being  developed 
which  grow  under  drier  conditions.  Rice  is  a  nutritious  food, 
and  the  water  in  which  it  is  cooked  is  said  to  contain  a  great  part 
of  the  nutriment.  Rice  is  the  principal  cereal  food  for  a  large  part 


Fig.  386. 
Barley  heads  (grown   at    Pullman,    Wash.). 


ECONOMIC   OR    USEFUL   PLANTS  397 

of  the  human  race.  It  contains  about  seventy-five  per  cent  starch, 
but  a  low  per  cent  of  proteid  matter,  which  is  more  fattening. 
Rice  is  therefore  a  good  food  in  hot  climates.  Most  of  the  rice 
in  this  country  is  polished  by  machinery  with  leather  rollers 
before  it  is  put  on  the  market.  This  pernicious  practice  removes 
the  outer  layer,  which  is  colored  (a  golden  yellow  in  the  Carolina 
rice,  and  sometimes  called  the  "  bloom  "),  and  also  removes  the 
most  nutritious  part  containing  the  proteids,  as  well  as  the  flavor.* 
561.  Indian  corn,  or  maize. — This  is  a  very  important  crop 
in  the  United  States.  Maize  (Zea  Mays)  was  cultivated  by  the 
Indian  tribes  in  America  from  early  times  and  is  supposed  to  be 
of  American  origin.  It  is  now  cultivated  in  Europe  and  other 
countries  (for  botanical  characters  see  Chapter  XVII).  Many 
varieties  are  now  known  which  are  grouped  in  certain  well-marked 
types,  as  dent  corn  with  a  prominent  indentation  at  the  free  end 
of  the  grain,  flint  corn  with  smooth  and  very  hard  kernels,  pop 
corn  noted  for  the  sudden  expansion  of  its  grains  into  a  large, 
light,  palatable  mass  under  the  influence  of  heat,  and  sweet  corn 
with  its  wrinkled  grains  containing  sugar  instead  of  starch  as  in 
the  other  varieties.  The  United  States  produces  four-fifths  of 
the  Indian  corn  grown  in  the  world.  While  it  is  grown  over 
quite  a  wide  latitudinal  range,  it  does  not  do  well  in  the  colder 
temperate  regions  because  of  the  short  cool  summers.  It  does 
best  in  rich  bottom  or  muck  soil  along  river  bottoms  in  warmer 
climates,  attaining  a  height  of  fifteen  to  twenty  feet  along  the 
Mississippi  River  and  in  the  Southern  States,  or  up  to  thirty 
feet  in  the  West  Indies,  while  dwarf  varieties  with  the  flint  grain 
succeed  better  in  the  extreme  northern  latitudes  of  its  range. 
Besides  the  use  of  the  grain  as  food  for  stock  and  man,  it  is  the 
source  of  much  of  the  whisky  in  the  United  States  and  most  of 
the  starch.  Sixty  per  cent  of  the  commercial  starch  is  obtained 
from  the  grains  of  corn.  The  grains  of  maize  contain  also  about 
five  per  cent  of  oil,  and  some  attention  is  given  to  its  extraction 
for  food  and  for  commercial  purposes.  The  blades  make  excel- 
lent fodder,  and  the  husks,  pith  and  cobs  are  used  in  the 
*  See  the  National  Geographic  Magazine  for  April,  1906. 


398 


GENERAL    MORPHOLOGY    OF    PLANTS 


manufacture  of  various  articles  (see  paragraph  442   for  smut  of 
corn) . 

562.  Sugar  cane,  sorghum,  broom  corn,  etc. — The  sugar 
of  commerce  is  largely  obtained  from  sugar  cane  (Saccharum 
officinaruni) ,  though  the  sugar  beet  is  also  the  source  of  a  great 
quantity.  The  sugar  cane  is  a  tropical  and  subtropical  member 


Fig.  387- 
Cutting  sugar-cane  in  Louisiana.      From  Louisiana  Agricultural  Experiment  Station. 

of  the  grass  family.  Louisiana  is  the  greatest  sugar-producing 
state  in  the  Union.  The  plant  is  ten  to  twenty  feet  high  and 
has  a  widely  spreading  panicle  of  flowers  at  the  top.  It  does  not 
produce  seed  in  the  United  States  but  is  grown  on  large  planta- 
tions from  cuttings.  The  canes,  after  being  stripped  of  the 
leaves,  are  crushed  to  obtain  the  sap,  which  is  boiled  down  to 
obtain  the  sugar  and  various  syrups  and  molasses.  Some  of 
the  great  sugar-growing  regions  are  Cuba,  Java,  the  Hawaiian 


ECONOMIC   OR    USEFUL   PLANTS  399 

Islands,  and  Louisiana.  Sorghum  is  a  somewhat  similar  cane 
grown  in  more  northern  latitudes,  where  it  seeds.  It  is  used  for 
making  certain  grades  of  molasses.  Broom  corn  (Sorghum  vul- 
gare),  an  allied  plant,  is  grown  for  the  stiff,  spreading  divisions 
of  the  panicle  which  are  used  for  making  brooms,  brushes,  etc. 

563.  Bamboo. — The  bamboo  canes  grow  in  tropical  and  sub- 
tropical countries,  where  they  attain  the  height  of  small  trees  and 
a  diameter  of  several   inches  to  a  foot.     The   stems  are  hard, 
light  and  strong.     They  are  used  for  building  purposes  and  for 
making  various  useful  articles.     There  are  several  species  used, 
but  the  most  common  and   widely  distributed  one  is  Bambusa 
vulgaris.     A  related  plant  (Arundinaria  macros perma) ,  the  giant 
cane,  forms  the  well-known  "  cane  brakes  "  along  river  bottoms 
in  the  Southern  States,  and  is  used  for  making  fishing  rods,  while 
split  bamboo  is  also  used  for  the  same  purpose. 

564.  The  palm  family  (Palmaceae). — The  members  of  this 
family  are  tropical  and  subtropical  plants,  and,  because  of  their 
beauty  and  grace  of  form,  many  are  grown  in  northern  latitudes 
indoors  for  ornamental  purposes.     A  common  example  in  the 
Southern  States  is  the  palmetto,  a  fan  palm,  which  is  the  emblem 
of  South  Carolina.     The  Washington  palm  of  Arizona  and  south- 
ern California  is  tree-like,  having  a  tall  trunk,  with  spreading 
leaves  at   the   top  forming  a  dense  mass.     It  grows  in  desert 
regions.     The  finest  palms  grow  in  the  tropics  and  are  the  most 
striking  and  characteristic  feature  of  the  landscape,  with  a  great 
variety  of  form  and  size.     Some  of  the  most  useful  palms  are 
as  follows.     The  cocoanut  palm  (Cocos  nuciferd)  always  occurs 
near  the  sea,  and  is  widely  distributed  in  all  tropical  countries. 
It  is  planted  to  some  extent  in  the  interior.     In  the  cocoanut  the 
outer  layer  of  the  fruit,  or  exocarp,   is  fibrous,  and  is  usually 
removed  in  the  preparation  of  the  fruits  for  commerce.     The 
fibrous  material  is  used  for  coarse  articles,  as  mats,  brushes,  cord- 
age, etc.     The  inner  layer  of  the  wall   (endocarp)  is  stony,  and 
at  one  end  are  seen  the  three  scars  indicating  the  compound 
nature  of  the  fruit,  since  it  is  composed  of  three  carpels.     The 
date  palm  (Phcenix  dactylifera)  is  a  native  of  Arabia,  is  cultivated 


400 


GENERAL   MORPHOLOGY   OF   PLANTS 


in  northern  Africa,  and  is  being  introduced  in  the  desert  and 
alkaline  regions  of  California  and  Arizona,  where  it  promises  to 
succeed.*  This  work  is  being  done  by  the  Department  of  Seed 
and  Plant  Introduction  of  the  United  States  Department  of  Agri- 
culture, which  is  already  producing  very  important  results  for 
agriculture  and  horticulture  in  this  country,  especially  in  the 


Fig.  388. 

Fruiting  date  palms  at  Old  Biskra,  Algeria,  with  fig  trees  growing  underneath.    From 
Bureau  Plant  Industry. 

arid  and  semi-arid  regions.  Because  it  is  adapted  to  grow  in  hot 
dry  regions,  it  becomes  a  valuable  crop  for  these  regions.  It  has 
a  short  stout  trunk  covered  with  the  old  leaf  bases,  while  at  the 
top  are  long  feathery  leaves.  Single  trees  sometimes  produce 
three  hundred  to  five  hundred  pounds  of  dates  in  a  season.  The 
flowers  are  in  dense  branched  panicles,  and  the  weight  of  the 
numerous  dates  later  bends  the  flower  stalk  downward,  forming 
a  graceful  cluster.  In  some  countries,  especially  along  the  Nile 
in  Egypt,  the  trees  are  all  numbered  by  the  Government,  and 

*  See  "  Our  Plant  Immigrants,"  in  National  Geographic  Magazine  for 
April,  1906. 


ECONOMIC   OR    USEFUL   PLANTS  40 1 

taxed.  The  sago  palm  *  (Metroxylon  Icems  and  M.  rumphii) 
produces  starch  which  is  sold  in  the  form  of  sago.  It  is  culti- 
vated in  the  East  Indies,  where  it  is  native.  The  starch  is  formed 
in  the  large  pith  of  the  trunk  and  several  hundred  pounds 
(500  to  800)  are  obtained  from  a  single  large  tree.  These  species 
produce  the  best  sago,  but  sago  starch  is  obtained  from  a  number 
of  other  palms.  Panama  hats  are  made  from  the  leaves  of  Cor- 
ludovica  palmata,  the  value  of  exports  from  Ecuador  alone  in 
1905  amounting  to  more  than  $600,000. 

565.  The  pineapple  family  (Bromeliaceae). — The  pineapple 
(Ananas   sativus)    is    native  to   tropical   America.     It   is  a  low 
plant   with    hard,    stiff,    narrow,   pointed   leaves  with   a  radiate 
arrangement.     The  fruit  is  borne  around  a  short  axis  above  the 
leaves.     It  is  cultivated  in  Florida,  which  furnishes  part  of  the 
supply  for  our  markets,  a  large  part  coming  also  from  the  West 
Indies    and    the    Bahama    Islands.     The    whole    flower    cluster 
becomes  a  fleshy  mass  forming  the  part  which  is  eaten.     The 
hanging  moss  (Tillandsia  usneoides)  belongs  to  the  same  family. 

566.  The  Lily  Family  (Liliaceae) . — This  h  one  of   the  most 
characteristic  families  of  the   monocotyledons,   since  the   flower 
parts  are  normal  and  well  developed,  not  having  undergone  the 
modification  shown  in  most  of  the  other  orders,     There  is  a  well- 
developed   perianth  of   six  parts  which  makes   the   most  showy 
part  of  the  flower.     The  members  of  the  family  are  nearly  all 
herbs  growing  on  the  ground.     Many  are  noted  for  the  produc- 
tion of    bulbs   or   root  stocks  containing  stored  food  providing 
for  the  rapid  and  early  growth  of  the  flower  stalk  in  the  early 
part  of  the  season.     The  Easter  lily  and  some  related  species  are 
grown   in   immense   quantities   in  tropical   countries   (Bermuda, 
Japan,  etc.)  and  the  bulbs  are  shipped  to  cooler  climates  to  plant 
in  greenhouses.     Other  cultivated  forms  are  tulips,  hyacinths,  etc. 
The  most  important  vegetable  products  for  food  in  this  family 

*The  Cycas  revoluta  is  sometimes  incorrectly  called  sago  palm.  But 
Japanese  sago,  a  coarse  starchy  material,  is  obtained  from  the  stems  of 
cycads,  and  a  sago  starch  is  also  obtained  from  Zamla  in  Jamaica  and 
Florida. 


402  GENERAL   MORPHOLOGY   OF   PLANTS 

are  the  onion  and  asparagus.  Fibers  are  obtained  from  the  New 
Zealand  flax,  a  member  of  this  family,  and  from  the  century  plant. 
Among  the  native  wild  species  may  be  mentioned  dog-tooth  violet 
or  adder's  tongue,  the  wild  lilies,  etc. 


Fig.  389- 

Cannabis  sativa.  Cutting  hemp  with  ordinary  mowing  machine.  A  horizontal  bar  attached 
to  an  upright  from  the  tongue  of  the  machine  bends  the  hemp  forward  in  the  same  direction 
that  the  machine  moves.  In  China  and  Formosa,  where  ramie  is  grown  commercially,  one 
stalk  is  cut  at  a  time,  leaving  the  younger  stalks  to  continue  their  growth.  Immediately  after 
cutting  the  stalk  the  bark,  including  the  fiber,  is  stripped  off  and  the  fiber  is  then  cleaned  by 
hand.  From  Fiber  Investigations,  U.  S.  Department  of  Agriculture. 

567.  The  banana  (Musa  paradisiaca)  should  be  mentioned 
among  other  useful  food  plants  of  the  monocotyledons.  The 
banana  is  a  native  of  tropical  countries  and  is  cultivated  for  its 
long  pod-like  fruits  which  are  seedless  in  the  commercial  variety. 
The  flowers  are  somewhat  related  to  the  orchids,  and  are  pro- 
duced in  a  long  terminal  spike,  the  large  fruits  hanging  in  dense 
heavy  clusters.  The  plant  is  like  a  small  tree  in  size,  with  broad 
and  long  strap-shaped  leaves.  One  of  these  "  plants,"  or  aerial 
shoots,  bears  but  once.  It  dies  down  and  a  new  shoot  is  rapidly 
developed  from  a  short  stout  root-stock.  The  banana  is  grown  in 
greenhouses  for  ornament,  and  the  commercial  variety  often  fruits 
here.  It  is  cultivated  to  some  extent  outdoors  in  the  extreme 
southern  parts  of  the  United  States,  but  our  chief  supply  comes 
from  the  West  Indies  and  Central  America.  Other  varieties 
for  ornament  are  grown  from  the  seed.  Manila  hemp  (Musa 
textilis)  is  cultivated  in  the  Philippines  for  the  fiber. 


ECONOMIC   OR    USEFUL   PLANTS 


403 


DICOTYLEDONES. 

568.  The  ament-bearing  plants.— These  include  three 
orders  which  resemble  each  other  in  that  the  flowers,  at  least 
the  staminate  ones,  are  in  aments  or  catkins.  The  flowers  are 
either  moncrcious  or  dioecious  and  very  much  reduced,  the 
floral  envelopes  being  reduced  to  mere  scales.  They  are  as 
follows:  The  willow  order  (Salicales),  including  the  willows,  pop- 
lars (Lombardy  and  trembling  poplars),  and  the  cotton  woods,  has 


Fig.  390. 

Cannabis  sativa.  Breaking  hemp  on  hand  brakes  in  Kentucky.  The  dark  stripes  across 
the  field  show  where  the  hemp  has  been  spread  for  retting.  After  lying  on  the  ground  from 
8  to  12  weeks  it  is  set  up  in  shocks  to  dry,  and  is  then  broken  and  the  fiber  cleaned  by  whipping 
it  across  the  brake.  One  man  with  a  hand  brake  will  average  about  75  pounds  of  cleaned 
fiber  per  day.  From  Fiber  Investigations,  U.  S.  Department  of  Agriculture. 

both  kinds  of  flowers  in  catkins.  Certain  willows  are  cultivated 
for  making  baskets.  The  walnut  order  (Juglandales)  includes 
the  walnut,  butternut,  and  hickory  trees.  The  staminate  flowers 
only  are  borne  in  catkins.  The  beech  order  (Fagales)  includes 
the  beech,  birch,  hazelnut,  alder,  oaks,  chestnut,  etc.  The 
staminate  flowers  here  are  also  in  catkins,  and  the  fruits  as 
acorns  in  the  oaks,  burs  in  the  chestnut,  etc.,  are  well  known. 
These  three  orders  include  many  valuable  trees  for  lumber,  the 
most  valuable  being  the  walnut,  hickory,  oaks,  beech,  birch,  and 


404 


GENERAL   MORPHOLOGY   OF   PLANTS 


cottonwoods,  and  form  a  large  part  of  the  deciduous  forest. 
Aside  from  the  amentiferous  trees  for  timber,  shade,  and  orna- 
ment, many  of  the  members  of  these  bear  nuts  which  form  an 
important  article  of  food  and  are  the  source  also  of  certain  kinds 


Fig.  391- 

Cannabis  sativa.  Hemp  brake  in  operation  at  Hanover,  Penn.  With  this  machine 
which  breaks  the  hurds  or  woody  portion  of  the  stalk  and  separates  it  from  the  fib  r,  four 
men  can  clean  from  800  to  1200  pounds  of  hemp  fiber  in  a  day.  From  Fiber  Investigations, 
U.  S.  Department  of  Agriculture. 

of  oil.  Most  of  these  nuts  are  well  known,  as  walnuts,  butter- 
nuts, pecans,  hickory  nuts,  hazelnuts,  filberts,  chestnuts,  and 
beechnuts. 

569.  The  nettle  family  (Urticaceae) -.—  Hemp.  The  hemp  h 
cultivated  for  the  fiber  and  derived  from  a  species  (Cannabis 
sativa)  native  to  central  Asia.  It  has  long  been  cultivated 
Europe,  and  has  become  naturalized  in  many  countries.  The 
fibers  are  the  fibro-vascular  bundles,  the  other  tissues  being 
removed  by  special  processes.  It  is  grown  to  some  extent  in  the 
United  States  for  fiber.  The  hemp  is  cut  with  an  ordinary  mow- 
ing machine,  as  shown  in  fig.  389;  an  elevated  horizontal  bar 
bends  the  stalks  forward  as  they  are  cut.  The  hemp  is  spread 
on  the  ground  for  "  retting."  Here  the  soft  tissues  are  disor- 


? 

m 


ECONOMIC   OR    USEFUL   PLANTS 


405 


ganized,  so  that  the  tough  elongated  fibers  are  easily  freed. 
After  lying  on  the  ground  for  eight  to  twelve  weeks  it  is  set  up  in 
shocks  to  dry  (fig.  390).  It  is  broken  and  cleaned  by  hand,  or 
by  machine  (figs.  390,  391).  Ramie,  also  called  China  grass,  silk 
grass,  ramie-hemp,  etc.,  is  the  fiber  from  a  shrub  (Bcvhmeria 
nivea)  native  in  China  and  the  Malay  Islands,  where  it  has  long 
been  cultivated  for  its  fiber,  which  is  used  for  making  fish  nets, 
cloth,  etc.,  while  in  China  and  Japan  some  beautiful  textile  fabrics 
are  made  from  it.  It 
is  cultivated  to  some 
extent  in  the  south- 
eastern United  States. 
The  name  hemp  is  also 
applied  to  fiber  used  for 
similar  purposes  and 
obtained  from  plants 
belonging  to  a  number 
of  different  families. 

Manila       hemp     COmeS        Agave  e,ongata<     sJ/LXe  henequen  plant  on- the 

from     i    Qnprips;    r»f    ha  dock,  ready  for  shipment  from  Progreso,  Yucatan.     The 

Da~  henequen  plant,  cultivated  in  Yucatan,  produces  more  than 

nana  ( lUT<u<:n  f0vfi]ir\r>nr\  nine-tenths  of  the  fiber  called  "sisal "  used  in  the  manufac- 

1  ture  of  binder  twine.    It  can  be  grown  successfully  only 

ic  pYfpnc;ivp1v  riiltivatpH  in  the  Tropics.     More  than  $33,000,000  worth  (Mexican 

iSlVCly  Cultivated  silvcr)  of  this  fiber  are  exported  from  Progreso  every  year, 

in     thp      Priilinninp      Tc      and  about  $15,000,000  worth,  gold,  are  imported  into  the 

rnillppme      IS-    United  States  to  be  used  chiefly  in   the    manufacture  of 

IcinrJc      U<xico1  "  f\r-  "ci'col     binder  twine.     From  Fiber  Investigations,  U.S.  Depart- 

lanas.     sisal,   or   sisal  ment  of  Agriculture, 
hemp,"   is    obtained 

from  the  henequen  plant,  a  species  of  Agave,  especially  Agave 
elongata.  It  is  grown  in  the  tropics,  a  large  quantity  being  grown 
in  Yucatan.  More  than  nine-tenths  of  the  "  sisal  "  used  in  mak- 
ing binder  twine  is  made  from  the  henequen  plant. 

570.  The  elm  family  (Ulmaceae)  includes  a  number  of  trees. 
Our  most  prominent  one  is  the  American  elm  (Ulmus  americana), 
a  large  tree  valuable  for  lumber.     It  is  much  planted  for  shade 
and  as  an  ornamental  tree.     It  is  one  of  the  most  rapidly  grow- 
ing trees. 

571.  The    mulberry   family   (Moraceae)    includes   the  mul- 
berry tree,  which  is  grown  for  its  fruit  and  as  a  shade  tree.     The 


406  GENERAL   MORPHOLOGY   OF  PLANTS 

paper  mulberries  furnish  from  their  bark  the  fiber  for  making  the 
beautiful  Japanese  paper. 

572.  The  fig  (Ficus  carica)   is  another  fruit  in    this  family. 
The  fig  is  cultivated   extensively  in   southern  Europe  and  Asia, 
and  to  a  slight  extent  in  some  of  the  Southern   States,  but  in 
California  it  bids  fair  to  become  an  important  addition  to  the 
great  fruit  industry  of  that   State  (paragraph  297).     Our  chief 
supply  comes  from  the  Mediterranean  region. 

573.  The  bread  fruit  (Artocarpus  incisa)  is  a  member  of  this 
family,  native  to  the  south  Pacific  Islands.     Recently  it  has  been 
introduced  in  tropical  parts  of  America.     The  tree  bears  a  round- 
ish fruit  four  to  eight  inches  in  diameter.     When  baked  it  much 
resembles  bread,  and  is  one  of  the  chief  sources  of  food  for  the 
natives  of  these  islands. 

574.  The  rose  family  (Rosacecc). — These  plants  are   culti- 
vated in  a  vast  number  of  varieties  chiefly  for  their  beautiful 
flowers.     Among   the   fruits   may   be   mentioned    the   following. 
Strawberries    (see    paragraph    327).     Like    all    of   our   common 
fruits  there  are  many  cultivated  varieties  of  strawberries.     They 
originated  from  the  species  native  in  Chili  about  two  hundred 
years  ago,  and  being  hardy  are  widely  distributed  from  tropical  to 
arctic  regions.     They  are  propagated  by  runners,  new  plants  for 
transplanting  being  obtained  from  the  young  ones  formed  where 
the  runners  strike  root.     Our 'native  wild  species  is  edible,  but 
has  not  been  successfully  cultivated,  nor  does  it  occur  in  suffi- 
cient quantity  for  market,  while  in  parts  of  Europe  wild  straw- 
berries are  abundant  and  are  found  in  the  markets  during  the 
entire  summer  season.     They   are  much   prized,  though    much 
smaller  than   the  cultivated  ones.    Raspberries  and  blackberries 
(aggregate  fruits,  see  paragraph  324)   are  shrubs,  and  are   also 
extensively  cultivated  in  many  varieties,  though  certain  wild  spe- 
cies produce  abundant  and  luscious  fruit  in  some  sections.     They 
are -propagated  by  cuttings  and  by  layers,  since  certain  species  prop- 
agate naturally  by  striking  root  where  the  tips  touch  the  ground. 

575.  The  apple  family  (Pomaces)  .—This   family  includes 
the  apples,   pears,  and  quinces.     These  are  called  pome  fruits 


ECONOMIC   OR    USEFUL   PLANTS  407 

(from  the  Latin  word  pomum,  a  fruit  or  apple).  They  are  all 
remarkable  for  the  beautiful  flowers  in  early  spring  as  well  as 
for  the  fruit  (see  paragraph  328  for  structure  of  the  fruit). 
Apples  were  derived  from  wild  species  of  Pirus,  occurring  in 
Europe  and  southwestern  Asia,  by  improvement  in  cultivation. 
From  one  of  these  species  came  the  many  varieties  of  our  com- 
mon apples,  and  from  the  other  came  the  varieties  of  crab  apples. 
North  America  now  leads  the  world  in  the  production  of  apples. 
It  is  our  most  valuable  fruit  because  of  the  great  number  of 
varieties  ripening  from  June  to  October,  with  a  great  variety  in 
flavor  and  keeping  qualities,  some  varieties  keeping  nearly  a  year 
after  maturity,  when  properly  stored.  They  are  now  more 
extensively  used  than  any  other  fruit  both  in  the  fresh  condition 
and  as  evaporated  fruits,  though  formerly  they  were  chiefly 
prized  for  the  making  of  cider  and  vinegar.  Apples  are  generally 
grown  over  the  country,  but  the  most  favorable  regions  are  the 
States  east  and  southeast  of  Lake  Michigan  as  far  as  Nova 
Scotia  and  Virginia,  the  region  about  Arkansas,  and  the  foothills 
of  the  Pacific  coast.  Pears  are  also  chiefly  derived  from  a  native 
European  species  of  Pirus.  The  trees  are  not  so  hardy  as  the 
apple  tree,  the  flowers,  twigs,  and  branches  being  more  subject  to 
blight,  a  bacterial  disease,  which  kills  and  blackens  the  affected 
parts,  though  the  apple  tree  is  sometimes  seriously  affected.  In 
some  sections  of  the  country,  especially  in  the  Middle  West,  the 
disease  is  more  serious  than  in  others,  and  successful  pear  culture 
is  more  limited  than  that  of  apples.  Quinces  are  chiefly  used  as 
preserves  and  to  flavor  other  fruits,  as  the  flavor  is  too  rich  and 
strong  for  relish  when  eaten  raw.  They  are  extensively  grown  in 
western  New  York,  and  are  subject  to  a  serious  disease,  the  leaf 
and  fruit  spot  (F^iomosporium  maculatum). 

576.  The  plum  family  (Drupaceae)  .—These  include  the 
drupes  or  stone  fruits  (paragraph  323).  The  principal  "stone 
fruits  "  cultivated  in  this  country  are  peaches,  plums,  apricots 
and  cherries.  Peaches  have  been  cultivated  from  time  immemo- 
rial in  China  where  they  were  native,  but  they  came  to  New 
York  by  way  of  Persia.  The  species  name  (Prunus  persica) 


408  GENERAL   MORPHOLOGY   OF   PLANTS 

refers  to  their  introduction  from  that  country.  The  fruit  is 
downy  (except  certain  smooth  varieties  known  as  nectarines)  and 
the  stone  is  corrugated.  The  flowers  of  many  varieties  are  con- 
spicuous and  beautiful,  though  many  of  the  recent  valuable 
varieties  have  rather  inconspicuous  flowers  because  of  the  small 
size  of  the  petals.  The  flower  buds  and  flowers  are  very  sensi- 
tive to  frost  and  extreme  cold  weather,  and  they  are  easily  killed 
during  a  severe  freeze  after  the  buds  have  begun  to  swell.  Warm 
seasons  during  mid-winter,  followed  by  very  low  temperature, 
sometimes  kill  the  flower  buds  before  they  open,  and  late  severe 
frosts  in  the  spring  also  kill  the  pistil  of  very  young  fruit  just 
before  or  after  the  flowers  have  opened.  This  limits  the  suc- 
cessful culture  of  peaches  to  certain  sections  where  natural  con- 
ditions modify  the  severity  of  the  cold,  as  near  large  bodies  of 
water  or  in  protected  localities.  The  best  peach-growing  sections 
in  the  United  States  are  along  the  eastern  and  southern  shores  of 
Lake  Erie  and  Ontario,  and  the  eastern  shore  of  Lake  Michigan, 
along  Long  Island  Sound,  the  Atlantic  Coast  and  Chesapeake  Bay, 
in  New  Jersey,  Delaware  and  Maryland,  in  the  milder  climates 
of  northern  Georgia,  Alabama,  .  outhern  Illinois  to  Kansas  and 
Missouri,  and  along  the  Pacific  Coast.  Plums  have  a  smooth 
skin  and  stone  and  there  are  a  great  many  cultivated  varieties. 
They  are  hardier  than  the  peach  and  thus  are  cultivated  over 
a  much  wider  area.  Prunes  are  varieties  cf  plums  which  are 
sweet,  and  are  dried  with  the  stone.  California  is  the  greatest 
prune-growing  section  in  this  country.  Apricots  resemble  a 
smooth  peach  and  have  a  smooth  stone  like  a  plum,  and  in 
external  appearance  resemble  both  a  plum  and  a  peach.  They 
were  native  of  China  or  Japan,  are  similar  to  the  peach  in  sen- 
sitiveness to  cold  and  are  not  extensively  cultivated  in  this 
country  except  in  California  and  in  parts  of  New  York.  The 
almond  is  closely  related  to  the  peach  and  originated  from  a 
species  (Prunus  amygdalinus)  probably  native  to  southern 
Europe.  It  is  chiefly  cultivated  in  the  Mediterranean  region, 
and  of  late  years  with  some  success  in  California.  The  flowers 
are  like  those  of  the  peach.  The  fruit  when  young  resembles  a 


ECONOMIC   OR    USEFUL   PLANTS 


409 


peach  but  the  exocarp  is  thin,  and  when  ripe,  cracks  open,  freeing 
the  nuts.  In  its  native  country  it  is  often  found  on  the  markets 
green.  It  is  eaten  in  this  condition  by  cutting  open  the  flesh  to 
secure  the  green  nut.  The  cultivated  cherries  are  derived  from 
two  species  native  to  Europe,  one  of  these  producing  the  varieties 
of  sour  cherries  which  are  extensively  grown  in  the  eastern 
United  States.  In  western  New  York  they  are  largely  grown 
for  canning.  The  sweet  cherries  form  a  large  and  tall  tree,  are 
also  grown  in  the  eastern  United  States,  but  most  extensively  in 
California.  The  native  species  in  this  country  have  small  fruits 
and  have  not  yet  shown  adaptability  to  improvement  in  cultiva- 
tion. One,  the  wild  black  cherry  (Prunus  serotina),  is  very 
valuable  for  lumber. 

577.   The  pea  family  (Papilionaceae) . — This  is  a  large  and 
important  family.     The  name  refers  to  the  supposed  resemblance 


Fig.  393- 

Peanuts  in  the  field,  showing  how  the  earth  is  drawn  up  to  cover  the  young  forming  pods; 
in  front  a  few  plants  pulled,  showing  the  peanuts.     From  Bureau  Plant  Industry. 

of  pea  flowers  to  a  butterfly  (Papilio).  The  flower  and  fruit  are 
described  in  paragraphs  249-251  and  320.  The  name  of  the  family 
is  sometimes  given  as  Leguminosa,  the  name  being  taken  from  the 
characteristic  fruit  which  is  a  legume  or  pod.  Many  of  the  mem- 
bers of  the  family  have  showy  flowers  and  are  grown  for  orna- 


410  GENERAL   MORPHOLOGY   OF   PLANTS 

ment,  as  the  wistaria,  sweet  pea,  etc.  The  sensitive  plants 
(Mimosa]  also  belong  here.  Peas  and  beans  are  important 
garden  and  field  crops,  there  being  many  varieties.  The  peas 
originated  from  southern  Europe  and  Asia.  The  lima  bean  was 
originally  a  native  of  South  America,  as  well  as  the  kidney  bean, 
from  which  the  common  bean  originated.  The  peanut  (also 
called  "  ground  nut  "  and  "  goober  ")  is  also  a  native  of  South 
America,  probably  Brazil.  It  is  extensively  cultivated  in  the 
Carolinas,  Georgia  and  Tennessee.  After  the  flowers  fall  the 
pod  turns  downward  and  pushes  into  the  loose  soil  where  the 
peanut  matures.  The  clovers  (Trifolium)  are  important  forage 
plants,  the  red  clover  being  the  most  important.  The  clovers, 
especially  the  white  clover,  are  visited  by  bees  for  honey,  and 
white  clover  honey  is  one  of  the  most  prized  kinds.  Alfalfa  is 
related  to  the  clovers  and  is  also  an  important  forage  crop,  espe- 
cially in  arid  regions  where  the  land  is  irrigated.  The  clover  and 
alfalfa,  as  well  as  peas,  are  often  used  for  "  green  soiling,"  and  all 
of  the  leguminous  plants  are  valuable  for  enriching  the  soil  in 
nitrogen  because  of  the  presence  of  the  nitrogen  fixing  organisms 
which  cause  the  tubercles  or  knots  on  the  roots  (paragraph  203) . 
There  are  some  valuable  trees  in  the  order,  especially  the  common 
locust  (Robinia)  valuable  for  timber  because  of  its  great  dura- 
bility. The  honey  locust  (Gleditsid)  is  noted  for  its  thorns  and 
is  cultivated  for  ornament.  The  red  bud  (Cercis)  is  grown  for 
ornament,  and  is  remarkable  for  the  numerous  dark  red  flower 
buds  which  "open  before  the  leaves  appear. 

578.  Flax. — The  flax  (Linum  usitatissimum)  is  a  member  of 
the  flax  family  (Linaceae)  and  is  an  important  fiber  plant.  The 
fiber  is  separated  from  the  stem  and  is  used  to  make  linen  thread 
and  cloth,  while  linseed  oil  is  obtained  by  pressure  from  the  seed. 
This  flax  is  native  in  the  Mediterranean  region  and  has  been 
cultivated  from  very  early  times.  It  has  been  long  cultivated  in 
the  United  States  for  oil,  and  recently  for  fiber  in  a  number  of 
the  northwestern  states.  Russia  leads  the  world  in  the  amount 
of  flax  grown,  while  Belgium  produces  the  finest  fiber.  Several 
species  of  wild  flax  are  native  to  the  United  States. 


ECONOMIC   OR    USEFUL   PLANTS 


411 


579.  Citrous  fruits. — The  citrous  fruits  belong  to  the  family 
Rutacece,  which  includes  also  our  native  prickly  ash  (Xantho- 
xylum) .  They  belong  to  the  genus  Citrus,  shrubs  or  small  trees 
native  in  tropical  and  subtropical  Asia.  Three  types  of  the 
citrous  fruits  are  cultivated  in  the  United  States.  The  culture 
of  the  citrous  fruits  is  often  attended  with  considerable  risk  be- 
cause of  hard  frosts  which  sometimes  nearly  or  quite  destroy 
the  crop,  or  even  kill  the  trees.  Experiments  are  now  in  prog- 


Fig.  394- 

Naval  orange  tree,  ten  years  old.     From  Bureau  Plant  Industry. 

ress  by  the  United  States  Department  of  Agriculture  which 
have  for  their  object  the  development  of  more  hardy  varieties. 
The  sweet  orange  has  been  crossed  with  Citrus  trifoliata  (which 
has  an  unedible  fruit) ,  and  the  result  is  a  hardier  tree  which  can 
be  cultivated  about  two  hundred  miles  farther  north  than  the 
present  limit  of  orange  culture.  A  number  of  varieties  have  been 
obtained  and  a  few  are  promising.  The  fruit  is  called  citrange. 
Two  varieties  give  promise  of  being  used  as  substitutes  for  lemons. 


412  GENERAL   MORPHOLOGY    OF   PLANTS 

Another  new  fruit,  tangero,  is  a  cross  between  the  tangerine 
and  grape  fruit,  in  which  the  qualities  of  the  two  fruits  are 
blended. 

580.  Oranges. — The  varieties  of  oranges  originated  from  one 
species   (Citrus  aurantium),   the  principal  forms  found   in   the 
market  being  sweet,  while  some  forms  are  bitter.     In  the  United 
States  they  are  cultivated  in  central  and  southern  Florida,  in 
California  and  in  the  delta  region  of  the  Mississippi.     The  seed- 
less naval  oranges  grown  in  California  were  introduced  in  1870 
from  Brazil  where  they  originated  as  a  seedling  variety.     The 
mandarins  or  "  kid  glove  oranges  "  belong  to  a  closely  related 
species  (Citrus  nobilis).     Some  are  small  and  of  a  light  orange 
color,  while  others  called  tangerines  are  dark  orange  or  red  and 
are  preferred  in  the  market  to  the  others. 

581.  Grape   fruits. — The   grape  fruits  were  derived  from  a 
species  (Citrus  decumana)  native  in  the  Malayan  and  Polynesian 
Islands.     Many  of  the  varieties  have  originated  in  Florida.     The 
fruit  is  rounded  in  form,  and  was  earlier  known  as  pomelo,  and 
sometimes  called  shaddock,  while  the  real  shaddock  is  a  different 
variety,  pear-shaped  and  little  used.     Grape  fruit  is  extensively 
cultivated  in  India,  Florida  and  California. 

582.  Lemons. — The  lemons  (Citrus  medico)  are  cultivated  to 
some  extent  in  Florida  and  California,  but  they  are  more  easily 
injured  by  cold,  and  our  chief  supply  comes  from  southeastern 
Europe  (Italy,  Spain  and  Portugal).     The  lime  is  a  variety  of  the 
lemon,  with  acid,  bitter  fruit  from  which  lime  juice  is  obtained. 

583.  The  maple  family  (Aceracea?)  has  inconspicuous  flowers 
and  the  fruit  is  called  a  key  fruit  or  samara.     Several  of  the 
maples   are   valuable   timber   trees.     The    hard   or   rock   maple 
(Acer  saccharum)  is  also  known  as  sugar  maple,  its  sap  yield- 
ing the  maple  sugar  of  commerce.     When  the  wood  is  full  of 
little  knots,  the  grain  of  the  lumber  is  very  beautiful  because  of 
numerous  concentric  rings.      It  is  then  known  as  "  bird's-eye  " 
maple,  and  is  much  prized  for  cabinet  work.     The  black  sugar 
maple  is  A.  nigrum.     The  soft  maple  (A.  saccharinum)   yields 
smaller  quantities  of  sap.     These  and  several  other  maples,  as 


ECONOMIC   OR    USEFUL   PLANTS 


413 


the  red  maple,  the  silver  maple,  box  elder,  etc.,  are  planted  for 
ornament  and  shade. 

584.  The  linden  family  (Tiliaceiu). — Our  well-known  repre- 
sentative  is   the   bass-wood    or   linden.     The   American    linden 
(Tilia  americana)   is  a  forest  tree  producing  a  soft  white  wood 
occurring    from    New    Brunswick    to    Georgia    and    Manitoba. 
The   white    bass-wood,  or  "  linn  "  tree    as  it   is  called    in    the 
South,  is    a   forest    tree    from  New  York  to  Florida  and  west 
to    Tennessee.      It    is    sometimes    called    "  bee-tree  "    and    is 
noted    for    the    fine    grade    of    honey    made    from    the  nectar 
in  the    flowers.       The    bast  (paragraph    98)    of    the  bass-wood 
trees   forms  long  and  stout  fibers.     The  bast,  or  Russian   bast 
as  it   is   sometimes  called  in  certain  trees,  is  used  for  making 
coarse  mats.     "  Jute  "  is  the  bast  from  certain  tropical  linden 
plants  (Corclwrus  olitarius). 

585.  The    mallow   family    (Malvaceae)    includes   the  holly- 
hocks,  mallows,   rose  of   sharon   (Hibiscus),   cotton,   etc.     The 


Fig.  395- 
Picking  cotton.     From  Bureau  Plant  Industry. 

cotton   plant   is  cultivated   for   the  fiber  on   the   seed.     Cotton 
(Gossypium)    is  the  most  important  fiber  plant  known.     The 


414  GENERAL   MORPHOLOGY    OF   PLANTS 

cultivated  varieties  were  derived  from  tropical  species.  One  of 
the  best  varieties  is  the  Sea  Island  cotton  (Gossypium  barba- 
dense  from  the  West  Indies)  which  has  very  long  fibers.  The 
best  quality  of  this  variety  is  cultivated  along  the  coast  of  South 
Carolina,  Georgia  and  Florida,  Upland  cotton  (Gossypium 
herbaceum,  probably  from  southern  Asia)  is  grown  back  from 
the  coast  over  a  wide  area  and  there  are  many  varieties.  The 
Sea  Island  cotton  is  what  is  called  a  long-staple  cotton,  because 
of  the  long  fibers.  Upland  cotton  is  a  short-staple  cotton,  the 
fiber  being  much  shorter  than  that  of  the  Sea  Island.  The  long- 
staple  cotton  is  necessary  for  some  purposes  and  the  Sea  Island 
cotton  in  consequence  is  worth  nearly  twice  as  much  as  the 
upland,  but  since  it  can  be  cultivated  over  such  a  small  area  as 
compared  with  the  total  cotton-growing  area  the  proportion  of  long- 
staple  cotton  is  small.  Efforts  have  been  made  to  cross  the 
long  and  short  staple  in  order  to  get  a  variety  of  cotton  with  a 
longer  staple  than  the  upland  which  can  be  grown  in  the  upland 
area.  A  variety  has  been  developed  which  is  improved  in  these 
respects.  Texas,  Louisiana,  Georgia,  Alabama,  Mississippi  and 
South  Carolina  are  the  greatest  cotton-producing  states,  but  it  is 
also  grown  in  Florida,  North  Carolina,  Kentucky,  Tennessee, 
Missouri  and  Arkansas.  India,  Egypt,  and  the  warmer  parts  of 
South  America  and  Russia  are  great  cotton-producing  countries. 
The  compound  pistil  forms  the  capsule  or  "  boll  "  as  it  is  called. 
The  fibers  are  attached  to  the  seed.  When  ripe  the  boll  bursts 
open  and  the  fluffy  white  mass  of  fiber  is  easily  "  picked."  The 
fiber  is  removed  from  the  seed  by  passing  it  through  a  machine, 
the  "  cotton  gin."  A  fine  grade  of  oil,  resembling  olive  oil,  is 
obtained  from  the  seed  by  pressure,  and  the  meal  left  is  used  as 
food  for  cattle,  and  for  fertilizer. 

586.  Chocolate. — Chocolate  or  cacao  is  obtained  from  the 
seeds  of  the  cacao  tree  (  Theobroma  cacao),  a  native  species  of 
Mexico  and  related  to  the  previous  order.  It  was  introduced 
into  Europe  by  the  Spaniards  and  is  cultivated  in  all  tropical 
countries.  The  cacao  is  expressed  from  the  seed,  heated  and 
moulded  into  cakes.  An  aromatic  substance  in  cacao,  known  as 


ECONOMIC   OR    USEFUL  PLANTS  415 

coca-butter,  is  used  in  medicine,  and  when  removed  from  the 
chocolate  leaves  coco,  which  for  some  persons  makes  a  more 
digestible  beverage  than  chocolate. 

587.  The  tea  family  (Theaceae)  is  represented  by  the  lob- 
lolly bay,  or  tan  bay  (Gordonia  lasianthus) ,  a  tree  with  coria- 
ceous evergreen  leaves,   and  large,  white,   solitary  flowers  often 
clustered  at  the  ends  of  branches.     The  tree  grows  from  West 
Virginia  to  Florida  in  low  woods,  and  flowers  from  May  to  July. 
Franklin's  tree  (G.  pubescens  =  Franklinia  altamahd),  a  native  of 
Georgia,    is  cultivated  as   an  ornamental   tree  as   far  north  as 
Massachusetts.     The    most    important    economic    plant    in    the 
family  is  the  tea  plant  (Thea).     Tea  is  a  native  shrub  of  sub- 
tropical Asia.     The  dried  leaves  are  used  for  making  the  well- 
known   beverage.     It  has  long  been   cultivated   in   China  and 
Japan,  and  was  introduced  in  cultivation  more  than  a  century 
ago  in  Java,   India  and  Ceylon.     Attempts  have  been  made  to 
cultivate  it  in  South  Carolina. 

588.  The  heath  family  (Ericaceae)  .—Examples  are  Labrador 
tea  (Ledum),  in  bogs  and  swamps  in  northern  North  America. 
The  azaleas,  with  several  species  widely  distributed,  are  beau- 
tiful flowering  shrubs,  and  many  varieties  are  cultivated.     The 
rhododendrons  are  larger,  with  larger  flower-clusters,  and  are 
also   beautiful   flowering   shrubs.     R.   maximum  occurs   in   the 
Alleghany  Mountains  and  vicinity,  from  Nova  Scotia  to  Ohio  and 
Georgia.      R.   catawbiense,  usually  at   somewhat   higher  eleva- 
tions,  occurs  in   Virginia  and   Georgia.     The   mountain   laurel 
(Kalmia  latifolia)  and  other  species  rival  the  rhododendrons  and 
azaleas  in   beauty.     The   trailing  arbutus   (Epig&a  repens),    in 
sandy  or  rocky  woods,  is  a  well-known  small  trailing  shrub  in 
eastern   North    America.      The    sourwood    (Oxydendrum    arbo- 
reum)  is  a  tree  with  white  racemes  of  flowers  in  August  and 
scarlet  leaves  in  autumn.     The  spring  or  creeping  wintergreen 
(Gaultheria  procumbens)  is  a  small  shrub  with  aromatic  leaves, 
and  bright  red,  spicy  berries. 

589.  The   huckleberry    family  (Vacciniaceae)   includes    the 
huckleberries    or  whortleberries   (example,  Gaylussacia  resinosa, 


41 6  GENERAL   MORPHOLOGY   OF   PLANTS 

the  black  or  high-bush  huckleberry,  eastern  United  States);  the 
mountain  cranberry  (Vaccinium  mtisidcea  =  Vitis-Idcea  vUisideea) 
in  the  northern  hemisphere;  the  bilberries  and  blueberries 
(Vaccinium)]  and  the  cranberries,  the  large  American  cranberry 
(Vaccinium  macrocarpon  =  Oxy coccus  macrocarpus]  in  the  cold 
bogs  of  North  America,  and  the  small  or  European  cranberry 
(Vaccinium  oxy  coccus  =  Oxycoccus  oxy  coccus]  in  northern  North 
America,  Europe  and  Asia. 

590.  The  olive  family  (Oleaceae)  includes  the  common  lilac 
(Syringa),  the  ash  trees  (Fraxinus),  some  of  which  afford  valu- 
able lumber,  the  privet  (Ligustrum,   used  for  hedges)   and  the 
olive  tree.      The  olive  tree  (Olea  europcsd)  is  a  native  of  the  Old 
World  and   has  been  cultivated   in  the   subtropical  regions  of 
Europe  and  Asia  from  early  times.     The  fruits,  which  resemble 
stone  fruits,  are  used  for  pickles  and  for  extracting  olive  oil.     The 
olive  is  cultivated  successfully  in  parts  of  California,  especially 
in  the  San  Joaquin  and  Sacramento  valleys  of  the  Coast  Range 
and  in  the  warm  belt  of  the  Sierra  Nevada. 

591.  The  potato  family  (Solanaceae) . — This  family  is  also 
known  as  the  nightshade  family  because  of  the  number  of  plants 
called   "  nightshade."     Many  .of  the  nightshades   have  an  evil 
smelling  foliage,  and  the  leaves  and  fruits  of  some  are  poison- 
ous.    Examples  are  ground-cherry,  belladonna,  henbane,  petunia, 
jimson-weed  or  thorn-apple,  matrimony  vine,  etc.     This  famib 
also    includes   several    important  cultivated   plants,  as   potato, 
tomato,  tobacco,  etc.     The  potato  (Solanum  tuberosum)  was  de- 
rived froin  a  wild  species  native  to  the  mountain  regions  of  the 
Western  Continent  from  Colorado  to  Chili.     It  was  cultivated 
by  the  native  Indians  before  the  discovery  of  America.    From 
here  it  was  introduced  into  Europe  and  has  been  so  extensively 
cultivated  in  Ireland,  where  it  is  one  of  the  most  important  foods, 
that  it  is  often  called  even  in  this  country  "  Irish  potato."     The 
subterranean  tubers  filled  with  starch  are  the  parts  of  the  plant 
used.     The  tomato  (Lycopersicum  esculentum]  originated  in  South 
America,  where  it  was  native  in  the  region  of  the  Andes  Moun- 
tains.     Many  varieties  are  now  known  which   are   extensively 


ECONOMIC  OR   USEFUL  PLANTS 


417 


cultivated  in  this  country  and  Europe,  though  the  greatest  pro- 
duction is  in  the  United  States,  where  it  is  used  raw  as  a  salad, 
or  cooked  in  various  ways.  Large  quantities  are  canned,  about 


Fig.  396- 

Tobacco  field  in  Virginia  at  harvest  time.  At  the  right,  showing  several  rows  cut  and 
lying  on  the  ground  to  wilt  before  hauling  to  the  curing  barn.  From  Tobacco  Investigations, 
Bureau  Plant  Industry. 

300,000  acres  annually  being  cultivated  to  supply  the  canning 
industry.  It  is  the  fruit  which  is  used.  Not  many  years  ago  it 
was  supposed  to  be  inedible,  was  grown  for  ornament,  and  called 


Fig.  397- 


Showing  sun  and  air  process  of  curing  tobacco  in  Virginia.     Part  of  the  tobacco  hung  in  the 
iring  barn.     From  Tobacco  Investigations,  Bureau  Pla 


lant  Industry. 


,    "  love   apple."      Peppers   and   egg   plants   are  related  species. 

Tobacco  (Nicotiana  tabacum)  belongs  to  the  same  family.     At 

,    the  time  of  the  discovery  of  America,  tobacco  was  found  in  culti- 


418  GENERAL   MORPHOLOGY   OF   PLANTS 

vation  by  the  Indians.  From  here  it  was  introduced  into  Europe, 
and  now  is  extensively  cultivated  in  the  warmer  parts  of  the 
world.  The  best  grades  are  grown  in  Cuba,  but  fine  tobacco  is 
also  grown  in  the  other  West  Indies,  in  Florida,  the  Philippines, 
Borneo,  Ceylon,  etc.  In  the  United  States  it  is  extensively  cul- 
tivated in  Florida,  Connecticut,  Pennsylvania,  Wisconsin,  Ken- 
tucky, Virginia,  North  Carolina,  Maryland,  Ohio,  Indiana,  Mis- 
souri, and  some  other  states.  The  leaves  of  the  tobacco  are  used, 
being  cured  by  drying. 

592.  Order  Rubiales,  the  madders. — There  are  three  families 
in  this  order.     The  madder  family  (Rubiaceae)  includes  the  bluets 
(Houstonia,   paragraph   292),   the  button  bush   (Cephalanthus), 
the  partridge  berry  (Mitchella),  the  bed  straws  (Galium),  etc.,  in 
this  country;  and  several  important  cultivated  plants  in  tropical 
countries.     The  coffee  plant   (C  off  em  arabica),  as  its  technical 
name   suggests,  is  a  native  of  Arabia,  but  is   now  cultivated  in 
many  other  tropical  countries  where  there  is  a  high  temperature 
throughout  the  year.     Brazil  now  leads  all  other  countries  in  its 
production.     Other  countries  where  it  is  extensively  grown  are 
Mexico,  Central  America,  Java,  Sumatra,  India,  Ceylon,  Arabia, 
Hawaiian    Islands,  West    Indies,  etc.     It    has   been   in   use   in 
Arabia  for  over  500  years.     The  "  beans  "  which  are  used  for 
making  the  beverage  are  seeds.     It  is  said  that  nearly  half  the 
coffee  produced  is  consumed  in  the  United  States.     Quinine  is 
obtained  from  the  bark  (Peruvian  bark)  of  trees  in  the  genus 
Cinchonia,  which  grow  in  South  America  chiefly  along  the  eastern 
slopes  of  the  v  estern  range  of  mountains.     The  trees  are  cultivated 
extensively  in  Java,  British  India,  Ceylon,  Japan  and  Jamaica. 

593.  The  honeysuckle  family  (Caprifoliaceac)  includes  the  elder  (Sam- 
hucus),  the  arrowwoods  and  cranberry  trees  (Viburnum},  the  honeysuckles 
(Lonicera),  etc. 

594.  Order  Valerianales  with  two  families  includes  the  teasel  family 
(Dipsacacea;).     Example,  Fuller's  teasel  (Dipsacus). 

595.  Order  Campanulales,  the  gourds  and  composites. — 

There  are  several  families  in  this  order.  The  most  important 
one  from  an  economic  standpoint  is  the  gourd  family  (Cucurbi- 


ECONOMIC   OR    USEFUL   PLANTS  419 

taceas),  which  contains  the  watermelons,  cucumbers,  musk- 
melons,  pumpkins,  etc.  The  floral  and  fruit  structures  of 
this  family  are  well  represented  by  the  squash.  The  musk- 
melons  have  been  derived  from  a  species  (Cucumis  melo) 
native  in  southern  Asia  but  is  now  cultivated  the  world  over. 
Large  crops  are  grown  in  New  Jersey,  Michigan  and  Colorado. 
The  two  principal  types  of  muskmelons  are  the  cantaloupes,  which 
are  elongated  and  have  a  furrowed  or  ribbed  rind,  and  the  nut- 
meg melons,  which  have  rinds  with  a  netted  sculpture.  Water- 
melons were  derived  from  a  species  native  in  tropical  Africa,  and 
have  been  cultivated  from  time  immemorial,  but  now  the  United 
States  leads  the  world  in  their  production.  They  are  grown  over 
a  large  part  of  the  United  States,  but  the  larger  markets  are 
chiefly  supplied  from  the  southeastern  states  (Georgia  especially). 
Cucumbers  (Cucumis  sativus)  are  native  to  southern  Asia,  and 
now  are  grown  in  different  parts  of  the  world.  They  are  chiefly 
used  for  pickles  and  are  extensively  grown  in  the  United  States. 
Pumpkins  (Cucurbita  pepo)  were  native  to  the  Western  Conti- 
nent, probably  originating  in  tropical  America.  Squashes  have 
originated  from  several  different  species,  some  from  the  same 
species  as  the  pumpkin  in  America,  and  others  from  species  native 
to  southern  Asia. 

596.  The  chicory  family  (Cichoriaceae)  includes  the  chicory 
or  succory  (Cichorium  intybus,  known  also  as  blue-sailors),  the 
oyster-plant  or   salsify   (Tragopogon  porrifolius) ,  the   dandelion 
(Taraxacum    densleonis  =  Taraxacum    taraxacum),    the    lettuce 
(Lactuca),    the    hawkweed    (Hieraceum),    and  others.      Lettuce 
(Lactuca  sativa)  is  cultivated  for  salad,  and  is  generally  supposed 
to  be  derived  from  one  of  the  compass  plants  (Lactuca  scariola, 
see  paragraph  132),  a  species  native  to  Asia.      Chicory  is  exten- 
sively cultivated  in  Europe  and  Asia.      The  fleshy  root  is  dried, 
roasted  and  ground,  when  it  is  used  as  a  substitute  for  coffee 
or  to  adulterate  it.     The  leaves,  after  being  bleached,  are  also 
used  for  salad. 

597.  The   thistle   family   (Composite)   includes   the   thistle 
(Carduus),     asters     (Aster),    goldenrods    (Solidago),    sunflowers 


420 


GENERAL   MORPHOLOGY   OF   PLANTS 


(Helianthus) ,  eupatoriums  or  joepye- weeds,  thoroughworts  (Eupa- 
torium);  coneflowers  or  black-eyed  Susans  (Rudbeckia),  tickseed 
(Coreopsis),  burmarigold  or  beggar-ticks  or  devil's-bootjack 
(Bidens),  chrysanthemums,  etc.  One  of  the  food  plants  is  the 
Jerusalem  artichoke  (Helianthus  tuberosus),  a  native  of  Canada 
and  the  upper  valley  of  the  Mississippi,  cultivated  for  the  fleshy 
tubers  or  root-stocks,  which  are  sweet  and  mealy.  It  was  for- 
merly grown  by  the  Indians.  In  the  globe  artichoke  (Cynara 
scolymus),  extensively  cultivated  in  Europe,  the  fleshy  bracts  of 
the  flower  head  and  the  young  portion  of  the  receptacle  and 
flowers  are  used  for  food. 


CHAPTER   XXXVII. 

RELATION    OF    PLANTS   TO    ENVIRONMENT 
OR   ECOLOGY.* 

598.  Influence  of   environment  on  the  life  processes  of 
plants. — By  environment  is  meant  all  those  conditions  or  factors 
outside  of  the  plant  which  in  any  way  influence  its  growth,  form, 
nutrition,   reproduction,   distribution,   etc.     The   relation   which 
some  of  these  conditions,  or  factors,  bear  to  the  plant  has  been 
quite  fully  studied  in  some  of  the  former  chapters.     For  example 
in  Chapter  XVIII  it  has  been  shown  how  the  pollination  of  plants 
is  largely   (in   most  cases   wholly)    dependent  upon   factors  or 
agencies  outside  of  the  plant,  as  in  cross  pollination  by  the  wind 
and  insects. 

I.    FACTORS    INFLUENCING    VEGETATIVE    TYPES. 

599.  These  conditions  of   environment  acting  on  the  plants 
are  factors  which  have  an  important  determining  influence  on  the 
existence,  habitat,  habit,  and  form  of  the  plant.     These  factors 
are  sometimes  spoken  of  as  ecological  factors,  and  the  study  of 
plants  in  this  relation  is  sometimes  spoken  of  as  ecology, -f  which 
means  a  study  of  plants  in  their  home  or  a  study  of  the  household 
relations  of  plants.     These  factors  are  of  three  sorts :  first,  physical 
factors;  second,  climatic  factors;  third,  biotic,  or  life,  factors. 

*  To  THE  TEACHER.  Chapters  XXXVII-XXXIX  are  intended  to  out- 
line the  subject  of  the  relation  of  plants  to  environment,  or  ecology,  and  to 
serve  as  the  basis  for  informal  talks  at  the  discretion  of  the  teacher,  or  parts 
may  be  assigned  for  reading  in  connection  with  some  of  the  studies  in  the 
earlier  chapters  in  the  book.  When  possible,  excursions  should  be  arranged 
to  the  fields  or  parks  where  many  of  the  principles  discussed  in  these  chapters 
can  be  illustrated.  Talks  by  the  teacher,  illustrated  by  lantern  views,  can 
also  be  given. 

f  OIKOS  =  house,  and  \6yos  =  discourse. 

421 


422  GENERAL   MORPHOLOGY    OF   PLANTS 

600.  Physical  factors. — Some  of  these  factors  are  water, 
light,  heat,  wind,  chemical  or  physical  condition  of  the  soil,  etc. 
Water  is  a  very  important  factor  for  all  plants.  Even  those 
growing  on  land  contain  a  large  percentage  of  water,  which  we 
have  seen  is  rapidly  lost  by  transpiration,  and  unless  water  is 
available  for  root  absorption  the  plant  soon  suffers,  and  aquatic 
plants  are  injured  very  quickly  by  drying  when  taken  from  the 
water.  Excess  of  soil  water  is  injurious  to  some  plants.  Light  is 
important  in  photosynthesis,  in  determining  direction  of  growth  as 
well  as  in  determining  the  formation  of  suitable  leaves  in  most 
plants,  and  has  an  influence  on  the  structure  of  the  leaf  accord- 
ing as  the  light  may  be  strong,  weak,  etc.  Heat  has  great  influence 
on  plant  growth  and  on  the  distribution  of  plants.  The  growth 
period  for  most  vegetation  begins  at  6°  C.  (=  43°  F.),  or  in  the 
tropics  at  10°  to  12°  C.,  but  a  much  higher  temperature  is  usually 
necessary  for  reproduction.  Some  arctic  algae,  however,  fruit  at 
i.8°C.  The  upper  limit  of  temperature  favorable  for  plants  in 
general  is  45°  to  50°  C.,  while  the  optimum  is  below  this.  Very 
high  temperatures  are  injurious,  and  fatal  to  most  plants,  but  some 
algae  grow  in  hot  springs  where  the  temperature  reaches  80°  to 
90°  C.  Som'e  desert  plants  are  able  to  endure  a  temperature  of 
70°  C.,  while  some  flowering  plants  of  other  regions  are  killed  at 
45°  C.  Some  plants  are  specifically  susceptible  to  cold,  but  most 
plants  which  are  injured  by  freezing  suffer  because  the  freezing  is 
a  drying  process  extracting  water  from  the  protoplasm  (see  para- 
graph 83).  Wind  may  serve  a  useful  purpose  in  pollination  and 
in  aeration,  but  severe  winds  injure  plants  by  causing  too  rapid 
transpiration,  by  felling  trees,  by  breaking  plant  parts,  by  deform- 
ing trees  and  shrubs,  and  by  mechanical  injuries  from  "  sand- 
blast." Ground  covers  protect  plants  in  several  ways.  Snow 
during  the  winter  checks  radiation  of  heat  from  the  ground  so 
that  it  does  not  freeze  to  so  great  a  depth,  and  this  is  very  im- 
portant for  many  trees  and  shrubs.  It  also  prevents  alternate 
freezing  and  thawing  of  the  ground,  which  "  heaves  "  some  plants 
from  the  soil.  Leaves  and  other  plant-remains  mulch  the  soil 
and  check  evaporation  of  water.  The  influence  of  the  chemical 


RELATION   OF   PLANTS    TO   ENVIRONMENT       423 


•'-A      '**?"» '      -f        '•      if.     -~-       •      -*>'+>     ' 

--•-''     ;  ei^wSft 


condition  of  the  soil  is  very  marked  in  alkaline  areas  where  the 
concentration  of  salt  in  the  soil  permits  a  very  limited  range  of 
species.  So  the  physical  and 
mechanical  conditions  of  the 
soil  influence  plants  because 
the  moisture  content  of  the 
ground  is  so  closely  depend- 
ent on  its  physical  condition. 
Rocky  and  gravelly  soil,  other 
things  being  equal,  is  dry. 
Clay  is  more  retentive  of 
moisture  than  sand,  and  mois 
ture  also  varies  according  to 
the  per  cent  of  humus  mixed 
with  sand,  the  humus  increas- 
ing the  percentage  of  moisture 
retained. 

601.  Effects  of  cold  and 
frost. — Intense  cold  prevents 

root  absorption,  and  has  a  drying  effect  on  vegetation,  so  that 
vegetation  protects  itself  in  several  ways  through  the  severe  winter 
in  temperate  and  arctic  climates.  The  deciduous  habit  of  trees 
and  shrubs,  the  underground  stem  of  perennial  herbs,  the  rosette 
habit  of  perennials,  the  bud-scales  on  winter  shoots,  and  the  low 
stature  of  arctic  and  alpine  plants  are  modifications  in  response 
to  the  harmful  effects  of  extreme  cold. 

602.  Effects  of  freezing. — In  freezing  weather  plants   are 
injured  in  three  ways:    First.  The  chilling  effect  of  cold  is  suffi- 
cient to  kill  some  plants  which  are  very  sensitive  to  low  temper- 
atures.    Second.  Others  are  killed  even  by  comparatively  light 
frosts,    or   freezes   (examples:    potatoes,    tomatoes,   corn,    many 
herbs,  young  leaves  and  shoots  of  many  plants).     In  these  cases 
the  injury  is  chiefly  caused  by  the  loss  of  water  from  the  pro- 
toplasm in  the  cells.     As  freezing  takes  place  in  the  tissues  the 
ice  crystals  are  usually  not  formed  within  the  cells.     But  some  of 
the  water,  under  the  influence  of  the  extreme  cold,  is  gradually 


Fig.  398- 

Main  trunk  straight,  branches  all  bent  and 
fixed  to  one  side  by  wind  from  one  direction 
(Rocky  Mountains). 


424  GENERAL   MORPHOLOGY   OF   PLANTS 

withdrawn  from  the  cells  into  the  intercellular  spaces  where  the 
ice  crystals  are  gradually  formed.  This  is  in  reality  a  protection 
to  the  protoplasm,  since  it  becomes  "  drier  "  and  thus  more  re- 
sistant to  cold.  When  the  plants  "  thaw  "  out,  if  the  protoplasm 
has  not  been  killed  by  the  cold,  this  water  may  be  absorbed  by 
the  protoplasm  again,  and  the  plant  is  not  injured.  Freezing, 
then,  to  a  certain  extent  has  the  same  effect  on  the  protoplasm 
as  the  loss  of  too  much  water  by  transpiration.  The  bud-scales 
thus  prevent,  the  loss  of  too  much  water  from  the  cells  of  the  deli- 
cate tissues  of  the  growing  point  of  shoots  in  winter,  although  in 
many  cases  freezing  in  these  tissues  takes  place.  Third.  In 
other  cases  plants  are  killed  by  the  actual  freezing  of  the  proto- 
plasm, though  there  are  some  plants  which  are  not  killed  by 
freezing  of  the  water  in  the  protoplasm. 

603.  Climatic    factors. — These    factors    are    operative   over 
very  wide  areas.     There  are  two  climatic  factors:    rainfall  or 
atmospheric    moisture,    and   temperature.     A   very   low   annual 
rainfall  in  warm  or  tropical  countries  causes  a  desert ;  an  abun- 
dance of  rain  permits  the  growth  of  forests ;  extreme  cold  prevents 
the  growth  of  forests  and  gives  us  the  low  vegetation  of  arctic  and 
alpine  regions. 

604.  Biotic,  or  life,  factors.* — These  are  animals  which  act 
favorably   in   pollination,   seed   distribution,   or   unfavorably   in 
destroying  or  injuring  plants,  and  man  himself  is  one  of  the  great 
agencies  in  checking  the  growth  of  some  plants  while  favoring  the 
growth  of  others.     Plants  also  react  on  themselves  in  a  multitude 
of  ways  for  good  or  evil.     Some  are  parasites  on  others;   some  in 
symbiosis  (see  paragraph  206)  are  aided  in  obtaining  food;  shade 
plants  are  protected  by  those  which  overtop  them ;  mushrooms 

*  These  biotic  factors  (plants  and  animals)  in  many  cases  do  not  exert  a 
personal  or  direct  influence  themselves  on  the  vegetation  concerned.  They 
often  merely  introduce  physical  factors,  as  shade,  etc.  But  in  some  of  the 
more  intimate  relations  of  plants  in  symbiosis,  parasitism  (one  form  of 
symbiosis),  etc.,  the  living  organism  as  a  factor  is  more  evident,  but  it  should 
be  understood  that  this  factor  is  not  in  the  nature  of  vitalism  in  the  sense 
of  the  old  vitalistic  theory. 


RELATION   OF   PLANTS    TO   ENVIRONMENT       42$ 


and  other  fungi  disintegrate  dead  plants  to  make  humus  and 
finally  plant  food ;  certain  bacteria  prepare  nitrates  for  the  higher 
plants  (see  paragraph  200) . 

II.     VEGETATION    TYPES    AND    STRUCTURES. 

605.  Responsive  type  of  vegetation.— In  studying  plants  in 
relation  to  environment  we  treat  rather  of  the  form  of  the  plants, 
which  fits  them  to  exist  under  the  local  conditions,  than  of  the 
classification  of  plants  according  to  natural  relationships.  Plant3 
may  have  the  same  vegetation  *  type,  grow  side  by  side,  and  still 
belong  to  very  differ- 
ent floristic  f  types. 
For  example,  the  cac- 
tus, yucca,  three- 
leaved  sumac,  the 
sage-brush,  etc.,  have 
all  the  same  general 
vegetation  type  and 
thrive  in  desert  re- 
gions. The  red  oaks, 
the  elms,  many  gol- 
denrods,  trillium,  etc., 
have  the  same  general 
vegetation  type,  but 
represent  very  differ- 
ent floristic  types 
since  they  belong  to  different  families  and  orders.  The  latter 
plants  grow  in  regions  with  abundant  rainfall  throughout  the 
year,  where  the  growing  season  is  not  very  short  and  tempera- 
ture conditions  are  moderate.  Some  goldenrods  grow  in  very 
sandy  soil  which  dries  out  quickly.  These  have  fleshy  or  succu- 
lent leaves  for  storing  water,  and  while  they  are  of  the  same 
floristic  type  as  goldenrods  growing  in  other  places,  the  vegetation 

*  i.e.,  the  stems,  leaves,  etc.,  are  of  a  kind  suitable  for  existence  under  the 
same  conditions. 

f  Flower-structure  type. 


Fig.  399- 
Bank  of  ferns.     (After  MacMillan.) 


426 


GENERAL    MORPHOLOGY    OF   PLANTS 


type  is  very  different.  The  types  of  vegetation,  which  fit  plants  for 
growing  in  special  regions  or  under  special  conditions,  they  have 
taken  on  in  response  to  the  influence  of  the  conditions  of  their 
environment.  While  we  find  all  gradations  between  the  different 
types  of  vegetation,  looking  at  the  vegetation  in  a  broad  way,  several 
types  are  recognized  which  were  proposed  by  Warming  as  follows  : 

606.   Mesophytes.*  —  These    are   represented   by   land   plants 
under  temperate  or  moderate  climatic  and  soil  conditions.     The 

normal  land  vegetation 
of  our  temperate  region 
is  composed  of  meso- 
phytes,  that  is,  the  plants 
have  mesophytic  f  struc- 
tures during  the  growing 
season.  The  deciduous 
forests  or  thickets  of  trees 
and  shrubs  with  their 
undergrowth,  the  mea- 
dows, pastures,  prairies, 
weeds,  etc.,  are  examples. 
In  those  portions  of  the 
tropics  where  rainfall  is 
great  the  vegetation  is 


the 


year 


mesophytic 
round. 
607  .    Xerophy  tes.  {— 

These  are  plants  which 
are  provided  with  struc- 
tures which  enable  them 
to  live  under  severe 
conditions  of  dryness, 

where  the  air  and  Soil  are 
^  ^   deserts   or 


Tropical  vegetation,  femsTnd  other  plants  growing 
around  and  upon  a  column  of  lava,  Hawaii. 


*  juesos  =  middle,  QVTOV  =  plant. 

t  Intermediate  between  the  structures  of  desert  and  water  plants. 

$  £e/oos  =  dry,  QVTOV  =  plant. 


RELATION   OF  PLANTS   TO   ENVIRONMENT       427 

semideserts,  or  where  the  soil  is  very  dry  or  not  retentive  cf  mois- 
ture, as  in  very  sandy  soil  which  is  above  ground  water,  or  in 
rocky  areas.  Since  the  plants  cannot  obtain  much  water  from  the 
soil  they  must  be  provided  with  structures  which  will  enable  them 
to  retain  the  small  amount  they  can  absorb  from  the  soil  and  give 
it  off  slowly.  Otherwise  they  would  dry  out  by  evaporation  and 
die.  Some  of  the  structures  which  enable  xerophytic  plants  to 


Fig.  401. 
Desert  society,  chiefly  cactus,  Arizona.     (Photograph  by  Tuomey.) 

withstand  the  conditions  of  dry  climate  and  soil  are  lessened  leaf 
surface,  increase  in  thickness  of  leaf,  increase  in  thickness  of 
cuticle,  deeply  sunken  stomates,  compact  growth,  also  succulent 
leaves  and  stems,  and  in  some  cases  loss  of  the  leaf.  Evergreens 
of  the  north  temperate  and  the  arctic  regions  are  xerophytes.* 

*  The  xerophytic  condition  of  the  conifers  is  probably  brought  about  as  a 
result  of  imperfect  vascular  system  of  the  stems.  There  not  being  true 
vessels  the  water  supply  to  the  leaves  is  scanty  and  slow.  The  leaves  are 
consequently  narrow,  thickened,  hard,  and  with  a  thick  cuticle.  This  offers 
an  excellent  example  of  correlation  (paragraph  656). 


428  GENERAL   MORPHOLOGY   OF   PLANTS 

608.  Hydrophytes.* — These  are  plants  which  grow  in  fresh 
water  or  in  very  damp  situations.  The  leaves  of  aerial  hydrophytes 
are  very  thin,  have  a  thin  cuticle,  and  lose  water  easily,  so  that 
if  the  air  becomes  quite  dry  they  are  in  danger  of  drying  up  even 
though  the  roots  may  be  supplied  with  an  abundance  of  water. 
The  aquatic  plants  which  are  entirely  submerged  have  often 
thin  leaves,  or  very  finely  divided  or  slender  leaves,  since  these 
are  less  liable  to  be  torn  by  currents  of  water.  The  stems  are 


Fig.  402. 
Pond  lilies,  Harlem  Lake,  Central  Park,  N.  Y.  City.     (After  Murrill.) 

slender  and  especially  lack  strengthening  tissue,  since  the  water 
buoys  them  up.  Removed  from  the  wrater  they  droop  of  their 
own  weight,  and  soon  dry  up.  The  stems  and  leaves  have  large 
intercellular  spaces  filled  with  air  which  aids  in  aeration  and  in 
the  diffusion  of  gases.  Some  use  the  term  hygrophytes. 

609.  Halophytes.f — These  are  salt-enduring  plants.  They 
grow  in  salt  water,  or  in  salt  marshes  where  the  water  is  brackish, 
or  in  soil  which  contains  a  high  per  cent  of  certain  salts,  for 
example  the  alkaline  soils  of  the  West,  especially  in  the  so-called 


*  vdop   =  water,  0urov  =  plant, 
f  dXos   =  salt,  <f>vrov  =  plant. 


RELATION   OF   PLANTS    TO    ENVIRONMENT        429 

"  Bad  Lands  "  of  Dakota  and  Nebraska,  and  in  alkaline  soils  of 
the  Southwest  and  California.  These  plants  are  able  to  with- 
stand a  stronger  concentration  of  salts  in  the  water  or  soil  mois- 
ture than  other  plants.  They  are  also  found  in  soil  about  salt 
springs. 


Fig.  403. 

Bad  Lands.  Pinus  ponderosa  scopularum  on  the  talus  of  huttes  on  the  borders  of  Sow- 
belly Canyon,  Pine  Ridge,  Nebraska.  Bouteloua  oligostachya  (grama  grass)  formation  in 
foreground  (Dept.  Geol.,  iv.  Nebr.). 

610.  Tropophytes.* — Tropophytes  are  plants  which  can  live 
as  mesophytes  during  the  growing  season,  and  then  turn  to  a 
xerophyte  habit  in  the  resting  season.  Deciduous  trees  and 
shrubs,  and  perennial  herbs  of  our  temperate  regions,  are  in  this 
sense  tropophytes,  while  many  are  at  the  same  time  mesophytes 
if  they  exist  in  the  portions  of  the  temperate  region  where  rain- 
fall is  abundant.  In  the  spring  and  summer  they  have  broad 
and  comparatively  thin  leaves,  transpiration  goes  on  rapidly,  but 
there  is  an  abundance  of  moisture  in  the  soil,  so  that  root  absorp- 
tion quickly  replaces  the  loss  and  the  plant  does  not  suffer.  In 

*  Term  used  by  Schimper,  T/SOTTOS,  from  Tpeireiv  =  to  turn,  (f>vTov=  plant. 


430  GENERAL    MORPHOLOGY   OF   PLANTS 

the  autumn  the  trees  shed  their  leaves,  and  in  this  condition  with 
the  bare  twigs  they  are  able  to  stand  the  drying  effect  of  the 
cold  and  winds  of  the  winter  because  transpiration  is  now  at  a 
minimum,  while  root  absorption  is  at  a  minimum  because  of  the 
cold  condition  of  the  soil.  Perennial  herbs  like  trillium,  den- 
taria,  the  goldenrods,  etc.,  turn  to  xerophytic  habit  by  the  death 
of  their  aerial  shoots,  while  the  thick  underground  shoot  which  is 
also  protected  by  its  subterranean  habit  carries  the  plant  through 
the  winter. 

611.  While  these  different  vegetation  types  are  generally 
dominant  in  certain  climatic  regions  or  under  certain  soil  con- 
ditions, they  are  not  the  exclusive  vegetation  types  of  the  regions. 
For  example,  in  desert  and  semidesert  regions  the  dominant  vege- 
tation type  is  made  up  of  xerophytes.  But  there  is  a  mesophytic 
flora  even  in  deserts,  which  appears  during  the  rainy  season 
where  temperature  conditions  are  favorable  for  growth.  This  is 
sometimes  spoken  of  as  the  rainy-season  flora.  The  plants  are 
annuals  and  by  formation  of  seed  can  tide  over  the  dry  season. 
So  in  the  region  where  mesophytes  grow  there  are  xerophytes, 
examples  being  the  evergreens  like  the  pines,  spruces,  rhododen- 
drons; or  succulent  plants  like  the  stonecrop,  the  purslane,  etc. 
Then  among  hydrophytes  the  semiaquatics  are  really  xerophytes. 
The  roots  are  in  water,  and  absorption  is  slow  because  there  are 
no  root  hairs,  or  but  few,  and  the  aerial  parts  of  the  plant  are 
xerophytic. 


CHAPTER   XXXVIII. 
MIGRATION    AND    DISTRIBUTION    OF    PLANTS. 

612.  The  migration  of  plants  is  the  movement  of  plants  over 
the  earth,  not  only  into  new  territory,  but  also  movement  from 
place  to  place  within  the  territory  already  occupied  by  a  given 
species.     The  word  distribution  is  sometimes  used  in  place  of 
the  word  migration,  and  is  also  used  to  indicate  the  area  already 
occupied  by  a  species. 

613.  One  very  important  principle  in  plant  migration  is 
that  of  the  pressures,  as  they  are  called,  which  are  behind  many 
of   the   plant   movements.     Plants   produce   great    quantities    of 
seeds  or  other  reproductive  bodies,  the  larger  number  of  which 
fail  to  make  new  plants.     These  seeds  are  scattered  yearly  from 
their  centers  of  production  so  that  whenever  a  chance  comes  for 
growth  the  seed  is  there  to  start  it.     In  the  area  occupied  by  the 
species  in  question  some  of  them  grow  to  new  plants  to  take  the 
place  of  those  which  perish.     Other  seeds  are  carried  beyond 
this  area  into  new  territory.     If  this  territory  is  suitable  for  the 
growth  of  the  species  in  question   it  may  gain  a  foothold  and 
thus  extend  the  "  range  "  of  the  species.     If  the  seeds  are  carried 
into  a  climate  unfavorable  for  this  species,  they  die.     This  great 
fertility  of  species  therefore  constitutes  a  pressure  which  is  ever 
forcing  the  species  onward  and  outward,   in  many  cases  into 
territory    where    it    cannot    possibly    obtain    a    footing.     Great 
changes  in  climate  also  produce  pressures  which  result  in  the 
migration  of  plants.     Some  of  the  principles  of  plant  migration 
may  be  considered  under  the  following  heads:    First,  methods 
and    causes    of    plant    migration;     second,    barriers    to    plant 
migration. 


432  GENERAL   MORPHOLOGY   OF   PLANTS 

I.     METHODS    AND    CAUSES    OF    PLANT    MIGRATION. 

614.  Advantages  of  plant  migration. — The  advantages 
accruing  to  plants,  through  their  power  or  tendency  to  migrate, 
is  that  individuals  of  a  species  are  increased  by  extending  their 
area  of  occupation.  Whether  the  plant  concerned  occupies  any 
given  area  to  the  exclusion  of  other  species  or  not,  an  extension  of 
the  area  provides  for  an  increase  in  individuals,  and  the  perpetu- 
ation of  species  is  thus  more  surely  safeguarded.  It  increases 
the  factor  of  safety  for  existence :  First.  By  the  larger  number 
of  individuals  possible  over  a  larger  area.  Second.  The  safety  of 
some  is  assured  in  case  of  disaster  to  others  in  a  certain  region. 
Disaster  may  come  by  sharp  competition  of  other  species,  or  by 
the  destructive  effect  of  physical  changes  in  the  topography  of 
certain  areas.  For  example,  in  time  of  flood,  areas  being  covered 
by  sand,  gravel,  or  other  rock  debris;  or  by  changes  in  the  climate, 
etc.  Third.  The  species  often  gains  in  vigor  by  coming  under 
new  conditions,  better  soil  conditions,  more  favorable  climate 
conditions,  etc. 

615.  Structural  characters  favoring  plant  migration. — 
Many  of  these  characters  are  discussed  more  fully  in  the  chapter 
on  "  Seed  Dispersal,"  and  others  in  the  chapter  en  "  Stems," 
etc.  The  mere  enumeration  of  some  of  these  characters  is  given 
here. 

1.  Seeds. — First.  The    buoyancy    of    seeds    produced    by    the 
development  of  so-called  "  wings  "  on  the  elm,  maple,  etc.,  the 
pappus  of  the  composites  and  other  hairy  or  wooly  outgrowths 
form  part  of  the  seed  or  fruit  which  enable  it  to  catch  the  wind. 
Small  size  and  lightness  of  many  seeds  also  give  them  a  certain 
amount  of  buoyancy.     Second.  The  development  of  structures  for 
grasping  hold  upon  other  objects;    for  example,  barbs  and  hooks 
on  seeds  or  fruits  for  clinging  to  animals.     Third.  The  use  of 
seeds  as  food  by  animals.     Fourth.  Seeds  which  are  capable  of 
floating  on  the  water. 

2.  Fruit. — There  are  many  fruits  which  are  used  for  food  by 
animals  and  the  seeds  of  which  often  pass  through  the  body 


MIGRATION   AND   DISTRIBUTION   OF   PLANTS      433 

uninjured,  and  thus  often  gain  wide  distribution,  especially  in  the 
case  of  migrating  birds.  Cedars  are  often  seen  growing  along 
fences  where  perching  birds  have  dropped  the  seeds.  Some 
plants,  like  those  of  the  mistletoe,  are  distributed  by  birds.  Ex- 
ploding fruits  also  bring  about  the  dispersal  of  seed,  as  in  the 
vetches,  the  touch-me-not,  the  fruit  of  the  witch-hazel;  or  of 
spores,  as  in  the  sporangia  of  ferns,  or  of  some  of  the  fungi. 

3.  Tumble-weeds. — Several  kinds  of  tumble-weeds  are  known, 
some  of  which  are  popularly  spoken  of  as  "  resurrection-plants," 
especially  certain  species  of  club-mosses  (Lycopodium).      These, 
as  is  well  known,  in  dry  weather  curl  their  stems  into  a  more  or 
less  round,  compact  ball,  and  in  so  doing  the  roots  are  frequently 
torn  from  their  attachment  to  the  soil,  and  the  ball  is  rolled  along 
by  the  wind  over  plains  to  considerable  distances.     During  the 
rainy  season  these  plants,  which  have  retained  their  life  in  the 
dry  condition,  expand  and  the  roots  take  hold  of  the  soil  again. 
Parts  of  plants,  as  the  seed-bearing  portion  of  certain  grasses, 
are  often  broken  during  heavy  winds,  and  are  blo\vn  or  rolled  for 
a  considerable  distance  over  the  ground,  thus  providing  for  the 
distribution  of  seed. 

4.  Floating  of  broken  branches. — In  the  case  of  certain  trees 
or  shrubs  growing  next  to  water  the  branches  are  often  broken 
by  the  wind  and,  floating  to  new  places,  sometimes  aid  in  the 
distribution  of  the  species. 

5.  Prostrate  creeping  plants  or  plants  with  a  more  rampant 
habit  migrate  through  a  system  of  natural  layering.     In  pros- 
trate or  creeping  plants,  like  the  strawberry,  or  trailing  roses,  the 
stems  take  root  here  and  there,  and  thus  slowly  and  surely  extend 
the  area  of  occupation  by  the  species.     Plants  of  more  rampant 
habit,    like    the    blackberries,    or   certain    roses,    take    root    at 
the  tips  of  their  branches,  where  they  come  in  contact  with  the 
ground,  and  new  shoots  develop  at  this  point.     This  habit  is 
sometimes    spoken    of    as    walking.     Example,    the    "  walking- 
fern  "  (fig.  302). 

6.  Underground  creeping  stems  or  roots. — Of  this  type  there 
are  a  large  number  of  well-known  examples  (the  underground 


434  GENERAL   MORPHOLOGY   OF   PLANTS 

shoots  of  many  grasses  for  example,  of  ferns  like  the  sensitive 
fern,  or  bracken  fern).  Among  those  which  extend  their  distri- 
bution through  roots,  a  striking  example  is  that  of  certain  species 
of  sumac.  In  New  York  state  several  species  of  sumac  by  their 
seeds  gain  foothold  in  abandoned  fields  or  in  pastures.  The 
roots  of  these  species  spread  many  feet  just  underneath  the  sur- 
face of  the  soil,  and  each  year  from  the  roots  new  shoots  are 
developed.  The  sumac  often  spreads  from  five  to  ten  feet  per 
year  in  this  way. 

616.  Causes  of  plant  migration. — The  plant  has  no  choice 
in  the  matter  of  migration  such  as  man  has.     In  the  vast  majority 
of  cases,  and  in  all  those  where  any  great  distance  is  covered,  the 
migration  of  the  plant  is  a  matter  of  accident  so  far  as  the  plant 
is  concerned.     The  plants  are  moved  from  one  place  to  another 
almost  wholly  by  physical  agencies,  by  changes  in  climate,  or  by 
the  agency  of  man  and  other  animals. 

The  work  of  man  in  plant  migration  is  carried  out  in  two  differ- 
ent ways:  by  design  and  by  accident.  The  history  of  agriculture 
and  horticulture  abounds  in  accounts  of  the  search  for  useful 
plants,  and  their  introduction  and  improvement.  Many  culti- 
vated species  have  thus  a  much  wider  range  and  grow  in  far 
greater  numbers  under  the  protection  of  man  than  could  ever 
have  been  possible  had  they  been  left  entirely  to  natural  causes. 
In  a  number  of  cases  the  plants  imported  for  cultivation  "escape" 
and  establish  themselves  as  "  wild  "  plants,  and  thus  become  an 
element  in  the  flora  of  the  region.  A  number  of  plants,  especially 
weeds,  are  introduced  from  one  country  to  another  by  accident, 
through  commerce.  Weed  seeds  may  be  accidentally  present 
with  grains  or  other  seeds  of  cultivated  plants,  or  in  the  straw 
used  for  packing.  In  other  cases  seeds  are  fraudulently  adul- 
terated by  designing  tradesmen;  so  that  it  has  become  necessary 
for  the  government  to  establish  a  seed  testing  laboratory  to 
examine  seeds  and  expose  these  fraudulent  methods. 

617.  Causes  of  plant  migration  initiated  by  plants  them- 
selves are  found  in:    First:  Fertility  of  species  by  which  seed 
results.     Plants  which  have  the  power  to  develop  large  numbers 


MIGRATION  AND   DISTRIBUTION   OF  PLANTS      435 

of  fertile  seeds  with  the  best  means  for  seed  distribution  not  only 
gain  distribution  through  the  seed,  but  by  the  crowding  of  cer- 
tain areas  bring  about  pressures.  Second.  The  centrifugal  habit 
of  self-propagation  by  runners,  by  layerings,  or  by  the  propaga- 
tion of  stems  from  separate  roots.  Third.  The  factor  of  adapta- 
tion to  environment,  or  acclimatization.  Other  causes  are  found 
in  physical  and  climatic  factors.  Some  of  these  have  already 
been  mentioned  under  the  head  of  structural  characters  favoring 
plant  migration,  ist :  There  are  certain  physical  factors,  as 
wind  and  water,  which  float  seeds  of  various  plants  to  great  dis- 
tances. Then  the  increase  of  depth  of  water  or  the  lowering 
of  depth  of  bodies  of  water  forces  to  a  limited  extent  migiation 
of  plants  along  other  shores.  2nd:  Tensions  in  fruits;  for  exam- 
ple, exploding  fruits. 

618.  Changes  in  climate  cause  migrations  of  plants. — 
Movements  of  plants  are  caused  by  changes  in  the  climate  which 
extend  over  long  periods  of  time.      The  most  noted  of  these 
influences  upon  plant  distribution  occurred  in  what   is  known 
as  glacial  times.     During  this  epoch  of  the  earth's  history  a  great 
ice-sheet  formed  in  Canada  and  British  America,  flowed  down 
across  the  border  and  over  a  great  portion  of  the  northern  United 
States.     This  great  change  in  the  climate,  the  intense  cold  for  so 
many  ages  gradually  extending  southward,  forced  the  plants  of 
northern  North  America  southward.     Those  which  were  not  able 
to  migrate  in  advance  of  the  glacier  perished.     As  the  ice-sheet 
reached  into  the  temperate  regions  it  forced  in  advance  of  it  the 
species  from   the   temperate   regions   southward.     Then  as   the 
glacier  retreated  northward  the  plants  which  were  able  to  survive 
by  southward  migration  again  migrated  northward.     Geological 
evidence  goes  to  show  that  there  were  a  number  of  movements  back 
and  forth  of  the  ice-sheet.     This  great  climatic  pressure,  therefore, 
fluctuated  for  long  periods,  forcing  the  plants  southward,  then 
again  yielding  and  allowing  the  plants  to  take  up  their  former 
positions,  when  again  they  would  be  forced  southward,  and  so  on. 

619.  Evidences  of  plant  migration  in  glacial  times. — In 
studies  of  the  distribution  of  the  plants  of  North  America,  Europe 


436  GENERAL   MORPHOLOGY   OF   PLANTS 

and  Asia,  there  are  at  present  evidences  of  this  migration  of 
plants  southward.  Many  arctic  plants  which  at  that  time  moved 
southward  are  now  left  on  the  higher  mountain  peaks,  or  in  the 
cool  sphagnum  moors  formed  among  some  of  the  terminal 
moraines.  With  the  proximity  of  the  continents  in  the  arctic 
circle  there  is  reason  to  believe  that  in  former  times  plants 
migrated  readily  between  the  continents  of  North  America, 
Europe  and  Asia.  During  glacial  times  these  were  forced 
southward,  in  Europe,  North  America  and  Japan.  Evidence  of 
this  is  shown  in  the  close  relationship  of  the  flora  of  northern 
Europe,  North  America  and  Japan.  Many  species  and  genera  of 
plants  found  in  these  countries  are  the  same.  Under  the  present 
conditions  of  the  climatology  of  the  earth  it  would  be  impossible 
for  the  plants  to  communicate  to  such  an  extent  as  to  explain 
the  presence  in  these  different  continents  of  such  a  large  number 
of  the  same  species.  While  in  the  seed  plants  there  are  many 
similarities  in  the  flora,  and  many  species  and  genera  are  iden- 
tical, in  the  lower  forms,  among  the  algae,  fungi,  liverworts  and 
mosses,  there  is  an  even  greater  similarity.  This  leads  us  to 
believe  that  even  microscopic  plants  like  the  fungi  and  algae 
migrated  under  these  conditions  along  with  the  seed  plants.  The 
parasitic  fungi  moved  along  with  their  hosts,  and  saprophytic 
fungi,  like  the  mushrooms,  followed  the  movements  of  forest 
trees,  growing  on  dying  or  dead  trunks,  upon  the  leaves,  and 
leaf-mold  in  the  forest.  The  aquatic  fungi  and  the  fresh-water 
algae  likewise  moved  southward  with  the  aquatic  flowering  plants. 
The  fact  that  so  many  of  the  fresh-water  forms  of  the  fungi  and 
algae,  as  well  as  of  the  flowering  plants,  are  identical  with  many 
of  those  in  northern  Europe  suggests  that  in  former  times  the 
continents  in  the  arctic  circle  were  very  near  together,  if  not  act- 
ually connected,  that  the  climate  was  milder,  and  that  there  was 
a  migration  of  these  fresh-water  plants  between  the  continents. 
This  might  be  brought  about  by  a  possible  continuity  of  land  and 
fresh-water  areas;  or  through  the  migration  of  water-fowl  the 
spores  of  algae  and  fungi  clinging  to  their  feet  could  be  trans- 
ported across  land  areas  or  channels  of  salt  water,  when  these 


MIGRATION  AND   DISTRIBUTION   OF  PLANTS      437 

were  not  too  wide,  and  lodged  in  the  fresh-water  pools,  or  lakes,  or 
streams  of  another  near-by  continent. 

620.  Present  climatic  pressures. — Other  climatic  pressures 
also  existed  and  continue  to  the  present  time.     In  the  humid 
tropics  large  numbers  of  individuals  of  different  species  are  prop- 
agated,  which   produce    a  pressure    northward   and  southward 
from  this  point,  but  those  moving  southward  on  the  northern 
hemisphere  come  in  contact  with  those  moving  northward,  and 
here   a  lateral  pressure   is  exerted  which  crowds  the  plants  to 
the  west  and  east.      Pressures  also  exist  in  the  borders  of  arid 
regions.     The  fertility  of  aggressive  species  wherever  they  occur 
tends  to  produce  pressures  in  all  directions. 

II.     BARRIERS    TO    PLANT    MIGRATION. 

621.  There  are  a  number  of  barriers  which  plants  meet  in 
their  migration  over  the  surface  of  the  earth.     In  general  terms 
we  might  speak  of  four  when  looking  at  the  world  as  a  whole. 
First.   Kinds  of  climate.    Regions  of  great  heat  or  cold,  of  dry- 
ness  or  moisture,  etc.    All  these  regions  oppose  obstacles  to  the 
entrance  and  passage  of  plants  which  are  accustomed  to  live  in 
different   climates.     Second.   Kinds   of  soil.    For  example,   the 
alkaline  deserts  and  the  great  salt  steppes  present  effectual  bar- 
riers to  the   passage  of  plants  not  provided  with   adaptations 
which  would  enable  them  to  live  under  such  extreme  conditions. 
Third.   Discontinuity  of  land.     Here  bodies  of  water  present  a 
barrier  to  the  passage  of  plants  from  one  continent  to  another, 
or  from  one  island  to  another,  which  are  separated  by  broad 
lakes  or  seas.     A  good  illustration  of  this  is  shown  in  the  relation 
of  the  continents  of  the  southern  hemisphere  as  compared  with 
those  of  the  northern  hemisphere  already  pointed  out.    Fourth. 
Mountain  chains.     High  mountain  chains,  because  of  the  great 
cold,  often  form  impassable  barriers  for  plants.    Good  illustrations 
of  this  are  shown  in  a  comparison  of  the  number  of  species  of 
plants  in   Europe   and  North  America  and  their    distribution. 
Under  the  high  climatic  pressures  which  existed,  for  example,  in 
glacial  times,  the  plants  of  North  America  met  with  no  barrier 


438  GENERAL   MORPHOLOGY   OF   PLANTS 

in  their  southward  movement;  probably  a  large  percentage  of 
them  survived.  In  North  America  the  mountain  chains  were 
parallel  with  the  migratory  movement  and  permitted  the  south- 
ward flow  and  return  of  the  species.  On  the  contrary,  on  the 
continent  of  Europe,  during  the  same  period,  in  their  southward 
movement  the  plants  met  with  an  impassable  barrier  in  the  Alps 
and  Pyrenees  mountains,  which  extend  east  and  west  across 
southern  Europe.  Many  of  the  species  thus  perished  and  were 
not  left  to  join  in  the  return  movement  in  populating  the  conti- 
nent after  the  disappearance  of  the  ice-sheet.  Likewise  the 
Alps  and  Pyrenees  presented  a  barrier  to  the  northern  movement 
of  the  plants  of  southern  Europe.  The  Rocky  Mountains  afford 
a  barrier  between  the  flora  of  the  Pacific  Coast  and  the  country  to 
the  east. 

622.  Conflict  of  species  in  migration. — This  is  one  of  the 
most  noticeable  features  in  plant  migration.  With  the  means  for 
movement  with  which  plants  are  provided,  together  with  the 
pressures  exerted,  forcing  them  to  move,  they  are  constantly 
reaching  out  for  new  territory  and  struggling  to  hold  that  which 
they  already  occupy.  The  competition  becomes  severe  because 
of  the  large  number  of  species  which  are  adapted  to  live  under 
similar  conditions.  Some  have  compared  the  struggles  of  plants 
to  occupy  new  territory,  or  to  maintain  their  hold  upon  their  own, 
to  the  competition  which  exists  among  human  societies.  Every 
plant  must  be  able  to  propagate  itself  and  to  hold  territory  in 
competition  not  only  with  climatic  conditions,  but  also  with 
other  plants  entering  the  same  region.  It  must  either  hold  its 
territory  or  cede  it  to  its  more  successful  rivals.  Thus  plants 
which  are  adapted  to  live  under  the  conditions  of  a  given  terri- 
tory are  those  which  survive,  while  the  weaker  ones  are  driven 
out,  or  exterminated,  or  occupy  a  very  subordinate  place  in  the 
society. 


CHAPTER   XXXIX. 
PLANT   SOCIETIES. 

623.  Plant  societies  are  associations  of  the  plants  of  an  area, 
over  which  the  conditions  are  similar.  Every  plant  society  has 
one  or  several  dominant  species,  the  individuals  of  which,  because 
of  their  number  and  size,  give  it  its  peculiar  character.  The 
society  may  be  so  nearly  pure  that  it  appears  to  consist  of  the 
individuals  of  a  single  species.  But  even  in  those  cases  there  are 
small  and  inconspicuous  plants  of  other  species  which  occupy 
spaces  between  the  dominant  ones.  Usually  there  are  several  or 
more  kinds  in  the  same  society.  The  larger  individuals  come 
into  competition  for  first  place  in  regard  to  ground  and  light. 
The  smaller  ones  come  into  competition  for  the  intervening 
spaces  for  shade,  and  so  on  down  in  the  scale  of  size  and  shade 
tolerance.  Then  climbing  plants  (lianas)  and  epiphytes  (lichens, 
algae,  mosses,  ferns,  tree  orchids,  etc.)  gain  access  to  light  and 
support  by  growing  on  other  larger  and  stouter  members  of  the 
society. 

Parasites  (dodder,  mistletoes,  rusts,  smuts,  mildews,  bacteria, 
etc.)  are  present,  either  actually  or  potentially,  in  all  societies, 
and  in  their  methods  of  obtaining  food  sap  the  life  and  health  of 
their  hosts.  Then  come  the  scavenger  members,  whose  work  it 
is  to  clean  house,  as  it  were,  the  great  army  of  saprophytic  fungi 
(molds,  mushrooms,  etc.),  and  bacteria,  ready  to  lay  hold  on 
dead  and  dying  leaves,  branches,  trunks,  roots,  etc.,  disintegrate 
them,  and  reduce  them  to  humus,  where  other  fungi  change 
them  into  a  form  in  which  the  larger  members  of  the  plant 
society  can  utilize  them  as  plant  food,  and  thus  continue  the 
cycle  of  matter  through  life,  death,  decay,  and  into  life  again. 
Mycorhizas  (see  paragraph  205)  or  other  forms  of  mutualistic 
symbiosis  occur,  which  make  atmospheric  nitrogen  available  for 

439 


440  GENERAL   MORPHOLOGY   OF  PLANTS 

food,  or  shorten  the  path  from  humus  to  available  food,  or  the 
humus  plants  feed  on  the  humus  directly.  Nor  should  we  leave 
out  of  account  the  myriads  of  nitrite  and  nitrate  bacteria  (see  para- 
graph 200)  which  make  certain  substances  in  the  soil  available  to 
the  higher  members  of  the  society.  Most  plant  societies  are  also 
benefited  or  profoundly  influenced  in  other  ways  by  animals,  as 
the  flower-visiting  insects,  birds  which  feed  on  injurious  insects, 
the  worms  which  mellow  up  the  soil  *  and  cover  dead  organic 
matter  so  that  it  may  more  thoroughly  decay.  In  short,  every 
plant  society  is  a  great  collection  or  gathering  of  multitudinous 
forms,  where  processes,  influences,  evolutions,  degenerations,  and 
regenerations  are  at  work. 

FOREST    SOCIETIES. 

624.  Different  kinds  of  forests. — We  know  that  the  mem- 
bers of  a  plant  community  vary.  Not  only  is  there  variation  in 
different  years  or  periods,  but  also  in  different  regions.  Regions 
which  are  so  widely  separated  as  to  show  great  climatic  differ- 
ences show  great  differences  in  the  character  of  plant  societies. 
The  same  is  true  of  the  forest.  Each  different  climatic  belt  or 
region  has  its  characteristic  forest.  For  example,  the  northern- 
most forests  are  chiefly  firs  and  balsams  with  here  and  there 
colonies  of  birches  and  aspens.  Next  to  these  come  extensive 
forests  of  the  white  pine  in  North  America,  and  also  hemlock. 
These  forests  of  firs  and  balsams  and  pines  extend  southward  on 
the  higher  mountains  because  it  is  an  extension  of  the  same  cli- 
matic belt.  Next  to  this  great  belt  of  conifers  is  a  great  belt  of 
the  hardwoods,  including  the  oaks,  hickory,  beech,  maples,  etc. 
The  forests  of  the  Rocky  Mountains  are  different  from  those  of 
the  Alleghanies,  because  of  the  great  barrier  of  the  plains  be- 
tween them  which  has  prevented  the  migration  of  species. 
Tropical  forests  are  different  from  those  of  the  temperate  re- 
gions. The  character  of  these  forests  depends  largely  on  climatic 
factors.  The  character  of  the  forest  varies,  however,  even  in 

*  See  Darwin,  Vegetable  Mould  and  Earth-worms. 


PLANT  SOCIETIES 


441 


the  same  climatic  area,  dependent  on  soil  conditions,  or  success 
in  seeding  and  ground-graining  of  the  different  species  in  com- 
petition, etc. 


Fig.  404. 

Mature  forest  of  redwood  (Sequoia  sempervirens).  Bureau  of  Forestry,  U.  S.  Dept.  Agr., 
Bull.  38. 

625.  General  structure  of  the  forest. —  Structurally  the 
forest  possesses  three  subdivisions :  the  floor,  the  canopy  and  the 
interior.  The  floor  is  the  surface  soil,  which  holds  the  rootage  of 
the  trees,  with  its  covering  of  leaf-mold  and  carpet  of  leaves, 
mosses,  or  other  low,  more  or  less  compact  vegetation.  The 
canopy  is  formed  by  the  spreading  foliage  of  the  tree-crowns, 
which,  in  a  forest  of  an  even  and  regular  stand,  meet  and  form  a 
continuous  mass  of  foliage  through  which  some  light  filters  down 
into  the  interior.  Where  the  forest  is  uneven  there  are  open 
places  in  the  canopy  which  admit  more  light,  in  which  case  the 
undergrowth  may  be  different.  The  interior  of  the  forest  lies 
between  the  canopy  and  the  floor.  It  provides  for  aeration  of 


442  GENERAL   MORPHOLOGY    OF   PLANTS 

the  floor  and  interior  occupants,  and  also  room  for  the  boles  or 
tree  trunks  (called  by  foresters  the  wood  mass  of  the  forest)  which 
support  the  canopy  and  provide  the  channels  for  communication 
and  food  exchange  between  the  floor  and  canopy.  The  canopy 
manufactures  the  carbohydrate  food  and  assimilates  the  mineral 
and  proteid  substances  absorbed  by  the  roots  in  the  soil;  and 
also  gets  rid  of  the  surplus  water  needed  for  conveying  food 
materials  from  the  floor  to  the  place  where  they  are  elaborated. 
It  is  the  seat  wrhere  energy  is  created  for  work;  and  also  the  place 
for  seed  production. 

626.  Longevity  of  the  forest. — The  forest  is  capable  of  self 
perpetuation,  and  except  in  case  of  unusual  disaster  or  the  action 
of  man,  it  should  live  indefinitely.     As  the  old  trees  die  they  are 
gradually  replaced  by  younger  ones.     So  while  trees  may  come 
and  trees  may  go,  the  forest  goes  on  forever. 

627.  Age  of  trees. — Many  trees  live  for  several  centuries.     A 
few  trees  are  known  which  have  lived  several  thousand  years. 
It  is  said  there  is  in  Kent,  England,  a  tree  of  the  genus  Taxus, 
3000  years  old;    also  that  there  are  now  living  on  the  slopes  of 
Mount  Etna  chestnut  trees  from  which  Homer  might  have  gathered 
nuts;  in  southern  Mexico  there  is  an  old  cypress  tree  (Taxodium) 
believed  to  be  about  6000  years  old,  and  in  the  Cape  Verde  Islands 
an  Adansonia  of  similar  age.     Another  account  states  that  this 
old  cypress  in  Mexico  is  about  2500  years  old.     It  is  difficult  to 
get  accurate  data  concerning  trees  of  such  age,  but  in  the  case  of 
the  big  trees  of  California  (Sequoia   washingtoniana)  data  have 
been  obtained  by  counting  the  annual  rings  of  a  number  of  trees, 
which  shows  their  age  to  range  up  to  4000  years. 

628.  Forests   do   not   materially   increase   rainfall   of  a 
region. — In  a  study  of  the  climatic  vegetation  regions  it  is  clear 
that  the  forest  is  dependent  on  rainfall,   and  below   a  certain 
minimum  annual  precipitation,  not  very  definitely  determined, 
forests  will  not  develop,  and  of  course  the  rainfall  must  be  rather 
evenly  distributed  throughout  the  year,  or  at  least  through  the 
growing  season.     But  that  the  rainfall  of  a  region  is  influenced 
by  the  forest  to  any  great  extent,  as  is  often  supposed,  is  not  so 


PLANT  SOCIETIES  443 

evident.  Long-continued  droughts  during  the  growing  season 
which  occur  now  and  then,  and  the  great  accompanying  forest 
fires,  show  the  inability  of  the  forest  to  produce  rainfall  per  se. 

629.  Importance  of  the  forest  in  the  disposal  of  rainfall. 
—The  importance  of  the  forest  in  disposing  of  the  rainfall  is  very 
great.  The  great  accumulation  of  humus  on  the  forest  floor 
holds  back  the  water  both  by  absorption  and  by  checking  its 
flow  so  that  it  does  not  immediately  flow  quickly  off  the  slopes 
into  the  drainage  system  of  the  valley.  It  percolates  into  the 


Fig.  405. 

Mountain  spring  in  forest,  fed  by  the  water  held  back  by  the  abundant  humus  and  dense 
undergrowth.     From  Bureau  of  Forestry. 


soil.  Much  of  it  is  held  in  the  humus  and  soil.  What  is  not 
retained  thus  niters  slowly  through  the  soil  and  is  doled  out  more 
gradually  into  the  valley  streams  and  mountain  tributaries,  so 
that  the  flood  period  is  extended,  and  its  injury  lessened  or  en- 
tirely prevented,  because  the  body  of  water  moving  at  any  one 
time  is  not  dangerously  high.  The  winter  snow  is  shaded  and 
in  the  spring  melts  slowly,  and  the  spring  freshets  are  thus 
lessened.  The  action  of  the  leaves  and  humus  in  retarding  the 
flow  of  the  water  prevents  the  washing  away  of  the  soil;  the 
roots  of  trees  bind  the  soil  also  and  assist  in  holding  it. 


444  GENERAL   MORPHOLOGY   OF   PLANTS 

630.  Absence  of  forest  encourages  serious  floods. — The 

great  floods  of  the  Mississippi  and  its  tributaries  are  due  to  the 
rapidity  with  which  heavy  rainfall  flows  from  the  rolling  prairies 
of  the  West  and  from  the  deforested  areas  west  of  the  Alleghany 
system.  The  serious  floods  in  recent  years  in  some  of  the  South 
Atlantic  States  are  in  part  due  to  the  increasing  area  of  deforesta- 


Fig.  406. 

Stone  Mountain  near  Atlanta,  Ga.,  the  ax  and  fire  having  removed  the  forest,  and  the 
heavy  rains  have  removed  the  soil  which  once  covered  the  larger  part  of  this  rocky  nob. 
From  President's  Message  in  relation  to  the  forests,  rivers,  and  mountains  of  the  Appalachian 
region,  1902. 

tion  in  the  Blue  Ridge  and  southern  Alleghany  system.  The 
aggregate  damage  from  floods  along  the  southern  Appalachian 
streams  in  the  year  1901-1902,  reached  the  sum  of  $18,000,000. 
A  movement  is  on  foot,  and  Congress  has  been  urged,  to  establish 
a  southern  Appalachian  Forest  Preserve,  and  it  is  to  be  hoped 
that  this  will  be  accomplished  (see  Message  of  President  Roose- 
velt to  Congress  concerning  this,  Washington,  1902). 

631.  Regeneration  of  forests. — If  the  forest  is  to  be  per- 
petuated there  must  be  regeneration,  or  in  time  all  trees  will  die 
and  the  forest  thus  become  extinct.  Natural  regeneration  takes 
place  in  two  ways:  first,  through  the  seed;  and  second,  by  the 
growth  of  sprouts  from  the  stump  when  the  tree  is  cut,  or  from 
the  roots.  These  sprouts  are  called  coppice.  Trees  which  are 


PLANT  SOCIETIES 


445 


shade-endurers  are  apt  to  have  the  advantage  in  the  natural 
regeneration  of  the  forest.  The  hemlock  spruce,  for  example,  is 
a  shade-endurer,  and  thus  the  seedlings  and  young  trees  in  the 
forest  stand  a  good  chance  of  coming  to  maturity.  The  redwood 
(Sequoia  sempervirens]  is  a  light-demander,  and  so  natural 
regeneration  by  seed  is  difficult  except  in  open  places.  The  red- 
wood, however,  develops  abundant  coppice,  and  the  great  amount 
of  nutriment  in  the  roots  of  the  large  trees  supplies  it  with  an 


Fig.  407. 
Coppice  from  redwood,  showing  sprouts  6  to  8  years  old.  (From  Bull.  38,  Bureau  of  Forestry.) 

abundance  of  food,  so  that  it  grows  rapidly,  the  stems  often 
becoming  quite  tall,  and  the  young  trees  remaining  white  except 
for  a  small  crown  of  green  leafage  at  the  top.  The  big  tree 
(Sequoia  washingtoniana)  regenerates  by  seed,  and  while  not  a 
great  shade-endurer,  enough  seedlings  survive  to  provide  a  suc- 
cession of  different  ages  where  lumbering  is  not  practiced. 


446  GENERAL   MORPHOLOGY   OF   PLANTS 

Very  few  of  the  other  conifers  can  develop  effective  coppice. 
They  are  dependent  on  the  seed  for  natural  regeneration.  On 
the  other  hand,  broad-leaved  trees  develop  abundant  coppice, 
and  in  this  respect  have  the  advantage  over  conifers,  which  are  not 
shade-endurers  or  do  not  develop  coppice.  Broad-leaved  trees 
are  limited,  however,  in  their  competition  with  conifers  on  thin, 
sandy  soil,  and  in  cold  regions,  because  many  species  of  the 
latter  can  grow  with  a  low  sum  total  of  heat. 

632.  Protection  of  forests.— The  fact  that  forests  have  an 
important  influence  in  regulating  the  movement  and  disposal  of 
rainfall   has   led   the    National    Government   and   several   State 
Governments  to  adopt  forest  policies  and  to  set  apart  certain 
forest  areas  as  reservations,  especially  in  mountainous  districts, 
where  lumbering  is  prohibited  by  law  and  efforts  made  to  regen- 
erate the  forests  where  necessary  and  protect  them  from  fire. 
The  value  of  these  forest  reservations  is,  first,  the  protection  of 
game  and  other  \vild  animals;    second,  holding  in  reserve  \vater- 
storage  for  power,  as  well  as  for  city  supplies;    third,  the  pro- 
tection  of   the    valleys    and   lowlands   from   destructive    floods; 
fourth,   the   providing   healthful  resorts  where  people  find  rest 
from   the   busy    and   exacting   professional   and   business   lives. 
When  the  principles  of  forestry  are  better  understood  by  the 
people  the  reservations  will  probably  be  cropped  and  regenerated 
according  to  some  suitable  system  which  will  not  lessen  their 
value  for  the  purposes  for  which  they  were  first  set  apart,  and 
at  the  same  time  will  yield  the  state  a  revenue  sufficient  to  more 
than  pay  for  the  cost  of  management,  and  also  will  tend  to  keep 
within  reasonable  bounds  the  prices  of  building  materials. 

OTHER    PLANT    SOCIETIES. 

633.  The  prairie  and  plains  societies. — These   are  to  be 
found  in  the  grassland  region.     In  the  prairies,  "  meadows  "  are 
formed  in  the  lower  ground  near  river  courses  where  there  is 
greater    moisture    in    soil.     The    grasses    here    are    principally 
"  sod-formers "  which  have  creeping  underground  stems  which 
mat  together,  forming  a  dense  sod.     On  the  higher  and  drier 


PLANT   SOCIETIES 


447 


ground  the  "  bunch  "  grasses,  like  buffalo  grass,  beard-grass,  or 
broom-sedge,  etc.,  are  dominant,  and  in  the  drier  regions  as  one 
approaches  desert  conditions  the  vegetation  gradually  takes  on 
more  the  character  of  the  desert,  so  that  in  the  plains,  sage-brush, 


Fig.  408. 

Winter  range  in  northwestern  Nevada,  showing  open  formations;  white  sage  (Eurotia 
lanata)  in  foreground,  salt-bush  (Atriplex  confertifolia)  and  bud-sage  (Artemisia  spinescens) 
at  base  of  hill,  red  sage  (Kochia  americana)  on  the  higher  slope.  (After  Griffiths,  Bull.  38, 
Bureau  Plant  Ind.,  U.  S.  Dept.  Agr.) 


the  prickly-pear  cactus,  etc.,  occur.  Besides  the  dominant  vege- 
tation of  the  society  there  are  subordinate  species,  and  the 
societies  are  especially  marked  by  a  spring  and  autumn  flora  of 
conspicuous  flowering  plants  which  are  mixed  with  the  grasses. 

634.  Desert  societies. — These  are  composed  of  plants  which 
possess  a  form  or  structure  enabling  them  to  exist  in  a  very  dry 
climate  where  the  air  is  very  dry  and  the  soil  contains  but  little 
moisture.  The  true  desert  plants  are  perennial.  The  growth 
and  flowering  period  occurs  during  the  rainy  season,  or  those 
portions  of  the  rainy  season  when  the  temperature  is  favorable, 
and  the  plants  rest  during  the  very  dry  season  and  cold.  Charac- 
teristic desert  plants  are  the  cacti  with  thick  succulent  green 
stems  or  massive  trunks,  the  leaves  being  absent  or  reduced  to 
mere  spines  which  no  longer  function  in  photosynthesis;  yuccas 


GENERAL   MORPHOLOGY   OF  PLANTS 

with  thick,  narrow  and  long  leaves  with  a  firm  and  thick  cuticle ; 
small  shrubs  or  herbs  with  compact  rounded  habit  and  small 
thick  gray  leaves.  All  of  these  structures  conserve  moisture. 
The  mesquite  tree  is  one  of  the  common  trees  in  portions  of  the 
Sonora  Nevada  desert.  Besides  the  true  desert  plants,  desert 
societies  have  a  rainy-season  flora  consisting  of  annuals,  which 
can  germinate,  vegetate,  flower  and  seed  during  the  period  of 
rain  and  before  the  ground  moisture  has  largely  disappeared, 
and  then  pass  the  resting  period  in  seed. 

635.  Conditions  with  which  desert  plants  contend. — The 
conditions  of  the  desert  are  very  austere,  so  that  plant  life  comes 
in  sharp  competition  with  the  climate.  The  principal  factors 
are: 

First,  the  very  low  rainfall,  varying  from  8  to  10  inches;  in  some 
deserts,  to  4  inches,  or  even  less  than  i   inch  in  some  areas. 
Second,  the  great  amount  of  evaporation  during  the  long,  dry, 
hot  season. 

Some  of  the  minor  factors  which  might  be  mentioned  are  as 
follows: 

First,  the  strong  light  (solar  radiation),  especially  during  the 
warm  season.  This  is  due  to  the  absence  of  clouds  which  form 
a  blanket  over  the  earth,  not  only  cutting  off  direct  solar  radia- 
tion during  the  day,  but  which  also  check  radiation  of  moisture 
from  the  soil  both  during  the  day  and  night. 

Second,  high  winds,  which  often  sweep  over  desert  areas, 
increasing  the  drying  effect  of  the  air  on  vegetation. 

Third,  the  physical  or  chemical  character  of  the  soil  often  is 
such  as  to  enforce  a  xerophytic  habit  for  vegetation  even  if  rain- 
fall were  greater;  for  example,  salty  or  alkaline  condition  of  the 
soil,  calcareous  soils  in  some  desert  or  semidesert  areas,  the  loose 
and  crumbling  condition  of  soil  in  some  regions  which  permits 
the  rapid  filtering  away  of  storm-  and  ground-water;  the  topog- 
raphy of  the  region  also,  when  very  rolling  or  hilly,  permits 
rapid  run-off  of  storm-water. 

636.  How  desert  plants  meet  these  conditions. — This  they 
do  by  provision  for:  First,  reduction  of  transpiration;  second, 


PLANT  SOCIETIES  449 

provision  for  water-storage;   and  third,  increased  surface  for  root- 
absorption. 

1.  Reduction  of  transpiration. — This  is  brought  about  in  several 
ways:  first,  by  reduction  in  size  so  that  the  leaves  are  smaller 
and  thicker;    second,  by  hairy  coverings;    third,   the   stomates 
are  sunk  deeply  in  the  surface ;  fourth,  the  cuticle  is  thickened ; 
fifth,  the.  leaves  are  entirely  dispensed  with  and  the  stems  are 
green  and  function  as  leaves;   sixth,  the  stems  are  shorter,  with  a 
thick  cuticle  and  often  hairy  or  waxy  coverings. 

2.  Provisions  for  water-storage. — This  is  provided  for  by  thick 
and  often  fleshy  leaves,  by  fleshy  stems  as  in  the  cacti,  and  often 
by  a  thick  root  system.     Some  of  the  cacti  have  large,  rounded, 
globose  stems.     Some  other  plants  have  large,  swollen  bases  to 
their  stems,   and  in  others  the  roots  are   also   much  enlarged. 
These  types  with  enlarged  roots  are  rather  rare  in  the  Sonora 
Nevada  desert  in  the  southwestern  part  of  the  United  States,  but 
are  more  common  in  southwestern  Africa  and  in  western  South 
America. 

3.  Increased  surface  for  root-absorption. — This  is  provided  for 
by  the  great  length  of  the  root  system  and  the  profuse  branching. 
In  many  desert  plants  the  roots  extend  to  great  depths  in  the 
soil,  where  they  obtain  ground-water  which  is  not  so  available 
nearer  the  surface. 

637.  Arctic-alpine  societies. — The  most  striking  of  the 
arctic  plant  societies  are  the  "  polar  tundra,"  extensive  mats  of 
vegetation  largely  made  up  of  mosses,  lichens,  etc.,  only  partially 
decayed  because  of  the  great  cold  of  the  subsoil,  and  perhaps 
also  because  of  humus  acid  in  the  partially  decayed  vegetation. 
These  tundras  are  brightened  by  numerous  flowering  plants 
which  are  characterized  by  short  stems,  a  rosette  of  leaves 
near  the  ground,  and  by  large  bright-colored  flowers.  Heaths, 
saxifrages,  and  dwarf  willows  abound.  Alpine-plant  societies 
are  similar  to  the  arctic,  although  some  of  the  conditions  are  more 
severe  than  in  the  arctic  region.  This  is  principally  due  to  the 
fact  that  during  the  summer  while  the  plants  are  growing  they 
are  subject  to  a  high  temperature  during  the  day  and  a  very  low 


450 


GENERAL    MORPHOLOGY    OF   PLANTS 


temperature  at  night,  whereas  during  the  summer  in  arctic 
regions  while  the  plants  are  growing  there  is  continuous  warmth 
for  growth  and  continuous  light  for  photosynthesis.  Five  types 
of  alpine  plants  are  recognized  by  some.  First.  Elfin  tree.  This 
type  has  short,  gnarled,  often  horizontal  stems,  as  seen  in  pines, 


Fig.  409. 
Polar  tundra  with  scattered  flowers,  Alaska.     (Copyright  by  E.  H.  Harriman.) 

birches,  and  other  trees  growing  in  alpine  heights.  Second.  The 
alpine  shrubs.  In  the  highest  alpine  belts  they  are  dwarfed  and 
creeping,  richly  branched  and  spreading  close  to  the  ground, 
while  at  lower  belts  they  are  more  like  lowland  shrubs.  Third. 
The  cushion  type.  The  branching  is  very  profuse  and  the 
branches  are  short  and  touch  each  other  on  all  sides,  forming 
compact  masses  (examples:  saxifrages,  androsace,  mosses,  etc.). 
Fourth.  Rosette  plants.  These  are  perennial,  with  short  stems 
and  very  strong  roots,  and  play  an  important  part  in  the  alpine 
meadows.  Fifth.  Alpine  grasses.  These  usually  have  much 
shorter  leaves  than  grasses  of  the  lowlands  and  consequently 
form  a  low  sward. 


PLANT   SOCIETIES 


451 


638.  Edaphic  plant  societies.— These  are  societies  the  plants 
of  which  are  chiefly  controlled  by  the  peculiar  conditions  of  the 
soil.  There  are  a  number  of  different  kinds  of  edaphic  plant 
societies  determined  by  the  character  of  the  physiographic  areas. 
First.  Sphagnum  moors.  These  are  formed  in  shallow  basins 
originally  with  more  or  less  water.  The  growth  of  the  sphagnum 


Fig.  410. 

Perennial  rosette  plant  from  alpine  flora  of  the  Andes,  showing  short  stem,    rosette  of 
leaves,  and  large  flower.     (After  Schimper.) 

moss  along  with  other  vegetation  and  its  partial  decay  in  the 
water  builds  up  ground  rapidly  so  that  in  course  of  time  the 
pond  may  be  completely  filled  in.  This  filling  in  proceeds  from 
the  shore  toward  the  center,  and  in  the  early  stages  of  course 
there  would  be  a  pond  in  the  center.  The  partial  decay  of  vege- 
tation creates  an  excess  of  humus  acid  which  retards  absorption 
by  the  roots.  The  conditions  are  such,  then,  as  require  aerial 
structures  for  retarding  the  loss  of  water,  and  plants  growing  in 
such  moors  are  usually  xerophytes.  Some  of  the  plants  are 
identical  with  those  growing  in  the  arctic  tundra.  Second. 
Sand  strand  or  beach*  The  quantity  of  sand  with  very  little  or 
no  admixture  of  humus  or  plant  food  makes  it  difficult  for  plants 
to  obtain  a  sufficient  amount  of  water  even  where  rainfall  is 
abundant.  The  same  may  be  said  of  the  sand  dunes  farther 
back  from  the  shore.  The  plants  of  these  areas  are  then  usually 

*  See  Chapter  LIV  of  the  author's  College  Text-book  of  Botany. 


452 


GENERAL    MORPHOLOGY    OF   PLANTS 


xerophytes.  Some  of  the  plants  accustomed  to  growing  in  such 
localities  are  American  sea-rocket,  seaside  spurge,  bug-seed,  sea- 
blite,  sea-purslane,  the  sand-cherry,  dwarf  willow,  marram- 
grass,  certain  species  of  beard-grass,  etc.  Third.  Rocky  shores  or 
areas.  Here  lichens  and  mosses  first  grow,  later  to  be  followed 
by  herbs,  grasses,  shrubs  and  trees,  as  decayed  plant-remains 
accumulate  in  the  rock  crevices.  Fourth.  Shores  of  ponds,  or 
swamp  moors.  Here  the  vegetation  often  takes  on  a  zonal 


i 

in. 


Fig.  411. 

Planting  grasses  on  wind-swept  sandy  coasts  to  prevent  movement  of  dunes  into  the 
city,  Southport,  England.     (Photograph  by  the  author.) 

arrangement  (zonation)  if  the  ground  gradually  slopes  to  the 
shore  and  out  into  the  pond.  In  fig.  412  is  shown  zonal  distri- 
bution of  plants.  The  different  kinds  of  plants  are  drawn  into 
these  zones  by  the  varying  amount  of  ground-water  in  the  soil, 
or  the  varying  depth  of  the  water  on  the  margin  of  the  pond  as 
one  proceeds  from  the  land  towards  the  deeper  water.  On  the 
border  lines  or  tension  lines  between  the  different  zones,  the 
plants  are  struggling  to  occupy  here  ground  which  is  suitable  for 
each  adjacent  individual  formation.  Other  edaphic  societies  are 
those  of  marl  ponds,  alkaline  areas,  oases  in  deserts,  warm  oases 


PLANT  SOCIETIES 


453 


454 


GENERAL   MORPHOLOGY   OF   PLANTS 


in  arctic  lands,  the  forested  areas  along  river  bottoms  in  prairie  or 
plains  regions,  etc. 

639.  Aquatic  plant  societies.  —  In  general  we  might  dis- 
tinguish three  kinds.  First.  Fresh-water  plant  societies,  with 
floating  algae  like  spirogyra,  cedogonium,  etc.,  the  floating  duck- 
meats,  riccias;  the  plants  of  the  lily  type  with  roots  and  stems 
attached  to  the  bottom  and  leaves  floating  on  the  surface,  like 
the  water-lily  and  certain  pondweeds,  and  finally  the  completely 


Fig.  413- 

Macrophytes  in  the  upper  zone  of  the  photic  region.    Ascophyllum  and  Fucus  at  low 
tide,  Hunter's  Island,  New  York  City.     (Photograph  by  M.  A.  Howe.) 

submerged  ones  like  certain  pondweeds,  the  bassweed  (Char a), 
etc.  Second.  Marine  plant  societies,  which  are  made  up  mostly 
of  the  red  and  brown  algae  or  "  seaweeds,"  though  some  green 
algae  and  flowering  plants  also  occur.  Third.  The  salt  marshes 
where  the  water  is  brackish  and  there  is  usually  a  luxuriant 
growth  of  marsh-grasses.  (See  Chapter  LV  of  the  author's 
College  Text-book  of  Botany.) 


CHAPTER  XL. 
SOME    PRINCIPLES  OF   PLANT    EVOLUTION. 

640.  Evolution  means  development  and  progress  accord- 
ing to  natural   laws. — It  is  growth   and  progress  from  very 
simple  conditions  or  things,  to  a  more  or  less  high,  complex  and 
perfect  condition,*  by  more  or  less  gradual  changes -which  take 
place  in  a  natural  way.     Looking  at  the  whole  period  of  de- 
velopment we  can  see  different  steps  in  the  progress  which  has 
taken  place. 

641.  If  we  look  at  the  progress  made  by  man  from  the 
savage  state  up  to  the  present  high  state  of  civilization,  we  can 
see  that  there  has  been  a  gradual  change,  a  progression  in  his 
relations  to  his  neighbors,  in  the  relations  and  dealings  of  com- 
munities, tribes   and  nations  with  each  other.     In  the  various 
arts,  trades,  and  manufactures  there  were  very  crude  beginnings, 
with  gradual  change  and  progressive  improvements  to  the  present 
time,  as  shown  by  the  many  inventions  and  the   high  state  of 
efficiency  in  the  trades  and  manufactures  at  the  present  time. 
All  this  has  come  about  by  evolution.     It  is  evolution  of  social 
man,  of  communities,  of  tribes,  of   nations;  evolution  of  trade, 
evolution  of  arts  and  manufactures.     It  would  have  been  impos- 
sible for  savage  man  or  for   the  early  civilized  men  to   invent 
and  build  at  once  the  many  highly  useful  and  efficient  appli- 
ances, the   means  for  transportation   and  communication,  etc., 
which  exist  to-day.     Very  crude  utensils,  appliances  and  build- 
To  THE  TEACHER.     This  chapter  is  intended  chiefly  for  reading  and 

reference.  It  can  serve  as  the  basis  for  informal  talks  by  the  teacher,  or 
portions  can  be  assigned  for  reading  at  his  discretion.  There  should  not  be 
any  attempt  to  commit  it  to  memory.  The  teacher  can  select  such  portions 
as  he  wishes  for  special  assignment. 

*  There  are  also  evolutions  downwards,  degeneration  or  retrogression. 

455 


456  GENERAL   MORPHOLOGY   OF   PLANTS 

ings  were  first  invented  by  early  man.  These  formed  the  basis 
for  improvement  and  further  invention,  so  that  there  has  been 
a  gradual  and  natural  growth  up  to  the  present  highly  efficient 
state  of  things.  This  is  evolution,  i.e.,  it  is  the  evolution  of  man 
and  his  work  from  the  savage  state  to  the  present  time.  History 
teaches  us  this.  But  in  parts  of  the  earth  man  still  exists  in 
the  savage  state.  So  there  are  half-civilized  tribes  where  crude 
and  very  inefficient  appliances  are  still  used.  So  among  the 
civilized  nations  there  are  shown  various  degrees  of  progress 
toward  the  condition  which  has  been  reached  in  the  most 
highly  civilized  nations.  The  present  savages,  semi-civilized 
tribes  and  less  civilized  nations  have  lagged  behind  in  this 
evolution.  Some  made  little  progress,  while  others  progressed 
for  a  time  and  then  stood  still.  Thus  we  have,  in  different 
parts  of  the  world  at  the  present  time,  living  examples,  which 
represent  some  of  the  steps  in  this  evolution  of  man  from  the 
savage  state. 

643.  Evolution  of  an  individual. — In  the  development  of  an 
individual  it  begins  as  a  single  cell.  By  growth  and  differen- 
tiation of  its  parts  it  finally  reaches  maturity,  completing  its  life 
cycle,  when  single  cells  are  formed  which  start  another  life  cycle. 
As  an  example  let  us  take  the  fern  plant.  The  asexual  spore 
from  the  spore  case  on  the  fern  plant  germinates  and  produces  a 
short  thread,  the  protonema,  or  first  thread,  which  resembles 
some  of  the  thread-like  green  algae.  The  end  of  this  thread  soon 
begins  to  expand  by  growth  and  cell  division.  It  now  forms  a 
thin,  flattened  mass  of  cells,  somewhat  heart-shaped  in  form, 
the  prothallium.  This  resembles  certain  thin  membranous  cell 
masses,  or  cell  plates  in  the  green  algae,  or  the  thallus  of  the  liver- 
worts. The  sexual  organs  are  next  formed,  and  then  the  egg  is 
fertilized.  The  fertilized  egg  now  divides,  and  in  its  early  stages 
recalls  the  very  young  embryo  of  the  liverworts,  but  it  soon 
departs  widely  from  the  course  of  development  shown  by  the 
liverworts  and  mosses.  Stem,  roots  and  leaves  are  developed. 
The  prothallium  which  lived  an  independent  existence  dies,  and 
the  fern  plant  becomes  an  independent  plant  able  to  carry  on 


SOME  PRINCIPLES  OF  PLANT  EVOLUTION        457 

its  nutrition  and  growth  of  mass,  finally  producing  spores  again 
which  complete  its  entire  life  cycle.  This  is  evolution  of  the 
individual*  There  is  change  and  progression,  in  a  natural 
way,  i.e.,  according  to  natural  laws. 

643.  There  are,  however,  different  steps  in  the  individual 
evolution  of  the  fern,  some  of  which  are  quite  clearly  marked, 
so  that  we  can  recognize  them.     We  can  also  recognize  that  they 
have  a  resemblance  to  lower  forms  of  plant  life.     The  asexual 
spore  recalls  the  single-celled  plants,  the  protonema  recalls  the 
thread-like  algae,  and  the  prothallium  recalls  green  tissue  plates 
or  membranous  masses  of  cells.     So  it  is  with  sexual  organs  and 
the  very  early  stages  of  the  embryo.     We  see  then  that  there  are 
plants  living  to-day  which  in  their  mature  condition  represent  or 
picture,  as  it  were,  some  of  the  different  stages  in  the  individual 
evolution  of  the  fern  plant.     Some  of  them  have  made  little 
progress  or  change  from  very  simple  one-celled  plants.     Others 
progressed  for  a  time  and  then  stood  still,  or  only  further  differ- 
entiation took  place.     They  have  lagged  behind,  and  thus  never 
reached  the  high  state  of  development  shown  in  the  fern  plant. 
The  seed  plants  show  a  still  further  progress  and 'a  higher  state 
of  development. 

644.  The  evolution,  or  life  history,  of  the  individuals  in  the 
different  groups  of  plants,  if  read  aright,  teaches  us  that  the 
higher  groups  have  been  built  on  the  experience  in  the  evolutions  or 
life  histories  of  some  of  the  lower  groups.     There  has  been  change 
and  progression  according  to  natural  laws  from  the  low  unicellular 
plants,  upward,  resulting  in  the  seed  plants,  the  dominant  vege- 
tation on  the  earth  at  the  present  time.     This  is  the  evolution  f  of 
higher  groups  from  the  lower  groups  along  lines  which  often  can 
be  traced,  as  regards  the  more  general  features.     So  it  is  with 
the   animal    kingdom;   the    higher    forms   have   been  developed 
from  the  lower  forms,  as  a  study  of  the  life  histories  or  evolu- 

*  Usually  called  Ontogenetic  evolution  (&v,  6i>ros  =  being ;  7^e<rt$  = 
generation  or  development). 

f  The  tracing  of  lines  of  evolution  from  lower  groups  to  higher  groups 
is  called  Phytogeny. 


458  GENERAL   MORPHOLOGY   OF  PLANTS 

tions  *  of  the  individuals  have  taught  us,  together  with  the  study 
of  fossil  forms  of  animals  and  plants  in  the  successive  geologic 
strata  of  the  earth,  as  well  as  the  method  of  distribution  of 
plants  and  animals  over  the  earth's  surface.  In  everything  where 
change  and  progress  takes  place,  evolution  is  manifest. 

645.  The  influence  of  Darwin  in  establishing  the  theory 
of  evolution. — To  Charles  Darwin,  probably  more  than  to  any 
other  one  man,  we  owe  the  evidence  which  has  led  to  the  general 
belief  in  the  theory  of  evolution  as  against  the  theory  of  the 
special  creation  of  species.  This  theory  has  been  accepted, 
because  it  appeals  to  the  mind  of  man  as  being  more  reasonable 
that  species  should  be  created  according  to  natural  laws  rather 
than  by  an  arbitrary  and  special  creation. 

Charles  Darwin  was  born  in  Shrewsbury,  England,  Feb.  12, 
1809,  and  died  in  1882.  At  an  early  age  he  showed  an  interest 
in  natural  science,  at  the  age  of  eight  years  becoming  interested 
in  insects.  In  his  sixteenth  year  his  father  sent  him  to  college 
to  study  medicine,  but  becoming  satisfied  that  his  bent  wras  in 
other  directions,  in  1828,  sent  him  to  Cambridge  University 
with  the  idea  of  his  eventually  becoming  a  clergyman.  His 
interest  in  natural  history,  making  collections  and  studies,  was 
continued.  By  the  encouragement  and  advice  of  some  of  his 
science  friends  in  the  faculty,  and  others,  he  was  led  to  devote 
more  attention  to  the  subjects  of  geology  and  natural  history. 
As  a  result  of  this,  at  the  age  of  twenty-two,  he  was  recommended 
to  the  captain  of  the  ship  Beadle,  who  wanted  a  young  naturalist 
to  accompany  him  on  a  scientific  exploration  in  different  parts  of 
the  southern  hemisphere.  This  was  the  real  beginning  of  his 
life  work.  His  collections  and  observations  on  this  voyage  led 
him  to  serious  reflection  on  the  origin  of  species. 

From  this  time  on  his  whole  life  was  devoted  to  careful  obser- 
vation and  study  of  the  habits  of  plants  and  animals,  their  vari- 

*  The  evolution  of  man  from  lower  animals  does  not  mean  that  man  was 
developed  from  the  monkey,  but  that  man  was  developed  from  some  being 
in  the  remote  past  which  was  probably  also  the  remote  ancestor  of  the  anthro- 
poid apes. 


SOME  PRINCIPLES  OF  PLANT  EVOLUTION        459 

ation  under  different  conditions,  as  well  as  the  causes  of  these 
variations,  and  the  natural  methods  by  which  certain  ones  sur- 
vived while  others  perished.  To  him  we  owe  the  elaboration  of 
the  theory  of  "  Natural  Selection "  as  one  of  the  important 
natural  laws  in  the  origin  and  differentiation  of  species,  though 
several  men  half  a  century  before  had  expressed  their  belief  in 
the  natural  origin  of  species. 

Darwin's  most  important  work  was  the  "  Origin  of  Species," 
first  published  in  1859.  This  work  was  the  result  of  twenty 
years  of  careful  study  and  observation  on  the  variations  of  plants 
and  animals,  both  wild  and  domesticated,  and  the  causes  which 
led  to  improvement  under  the  control  of  man,  as  well  as  in  a 
state  of  nature.  His  great  work  here  consisted  in  the  vast  amount 
of  evidence  which  he  presented  in  favor  of  the  natural  origin  of 
species,  that  species  vary,  and  where  these  variations  are  bene- 
ficial, natural  selection  preserves  the  forms  which  possess  them 
while  it  destroys  the  others. 

^646.  Mendelism,  or  mendelian  hybrids. — Gregor  Mendel, 
born  in  Briin,  Austria,  in  iS^^discovered  the  law  governing  this 
kind  of  hybrids.  He  was  a  monk,  and  afterward  became  the 
Abbot  of  Briin.  He  discovered  this  law  during  his  experiments 
on  plant  hybridization,  and  published  an  account  of  this  in  the 
Natural  History  paper  of  his  town.  This  work  did  not  become 
widely  known  at  the  time,  and  the  paper  was  only  recently  redis- 
covered and  published,  so  that  it  became  accessible  to  all  workers 
in  plant  breeding.*  It  was  a  very  interesting  discovery  as  well 
as  being  of  great  importance  to  the  plant,  breeder.  Mendel 
worked  chiefly  with  peas.  Two  examples  will  be  given  here  to 
serve  as  illustrations  of  the  principle. 

He  selected  two  varieties  of  peas  which  differed  in  one  being 
tall  and  the  other  a  dwarf.  These  were  cross  pollinated.  The 
seeci  from  the  cross  was  sown  the  following  year,  and  all  the 
progeny  resembled  the  tall  parent,  i.e.,  all  of  the  first  generation 
of  hybrids  were  tails,  and  no  sign  of  the  dwarf  character  could 

*  See  Bateson,  Mendel's  Principles  of  Heredity;  also  Punnet,  R.  C., 
Mendelism. 


460 


GENERAL   MORPHOLOGY   OF   PLANTS 


be  seen.  But  in  the  second  generation  of  hybrids  (from  seed  of 
the  first)  tails  and  dwarfs  were  both  present,  and  in  the  pro- 
portion of  twelve  tails  to  four  dwarfs.*  The  tails  of  the  first 
hybrid  generation,  then,  contained  the  dwarf  character  as  wrell 
as  the  tall  character,  but  the  tall  is  the  dominant  character 
and  prevented  the  dwarf  from  expressing  itself.  The  dwarf 
character  was  latent. 

On  planting  seeds  of  this  second  hybrid  generation,  dwarfs  and 
tails  being  kept  separate,  the  dwrarfs  \vere  shown  to  be  pure 
dwarfs,  and  in  all  the  succeeding  generations  produced  nothing 
but  dwarfs.  This  showred  that  out  of  every  sixteen  of  the  second 
generation,  four  dwarfs  were  "  extracted."  The  dwarf  character  is 
the  recessive  character.  A  study  of  the  tails  of  the  second  hybrid 
generation  showed  also  that  for  every  sixteen  of  the  second  gen- 
eration there  were  four  tails  extracted,  which  thereafter  always 
produced  tails.  The  other  eight  tails  of  the  second  generation 
had  both  the  tall  and  dwarf  character,  but  in  the  third  genera- 
tion split  up  so  that  for  every  sixteen  there  were  twelve  tails  and 
four  dwarfs,  and  so  on.  This  can  be  shown  by  the  following 
diagram. 


ist  Hybrid                2nd  Hybrid            3rd  Hybrid 

4th  Hybrid 

Generation               Generation            Generation 

Generation 

• 

'25%  pure        =  100%  pure     = 

=  1  00%  pure 

tails                 '    tails 

tails 

25%  pure 

=  100%  pure 

tails 

tails 

'25%     pure 

tails 

1  00%     mixed 

50%       mixed  « 

50%     mixed 

50%  mixed 

tails 

tails 

tails 

tails 

-  5%      Pure 

dwarfs 

125%    pure 

-=  100%  pure 

dwarfs 

dwarfs 

25%  pure          =  100%  pure 

=  100%  pure 

dwarfs                 dwarfs 

dwarfs 

Tall  plant 


Dwarf  plant 


*  They  do  not  always  come  out  in  such  exact  mathematical  proportions, 
but  when  the  number  of  plants  grown  is  large,  the  proportion  is  very  close  to 
this. 


SOME  PRINCIPLES   OF  PLANT  EVOLUTION        461 

Characters  which  behave  in  this  way  are  called  unit  characters. 
Mendel  studied  the  relation  of  other  unit  characters  of  the  pea, 
and  found  that  smooth  seeds  are  dominant  to  wrinkled  seeds, 
colored  are  dominant  to  white,  yellow  color  dominant  to  green, 
etc.  Where  two  unit  characters  in  each  parent  are  contrasted 
the  result  is  still  more  interesting  because  it  results  in  the  pro- 
duction of  two  new  forms.  For  example,  he  crossed  tall  yellow 
peas  with  dwarf  green  peas.  The  result  was  that  in  the  first 
hybrid  generation  all  were  tall  yellows.  But  in  the  second 
hybrid  generation  they  split  up  with  the  following  result.  For 
every  sixteen  plants  there  were  nine  tall  yellows,  three  dwarf  yel- 
lows, three  tall  greens,  and  one  dwarf  green.  It  will  be  seen  that 
the  dwarf  yellows  and  tall  greens  are  new  forms,  and  successive 
generations  show  that  these  can  be  extracted  and  grown  as  pure 
forms.  This  is  a  very  important  discovery  for  it  enables  the 
plant  breeder,  after  he  has  determined  by  experiment  what  the 
unit  characters  of  his  plants  are,  to  combine  certain  desirable 
characters  in  a  single  form  (paragraph  663). 

647.  Mutation. — Mutation  is  the  term  applied  to  those 
sudden  variations,  not  due  to  cross  fertilization,  in  which  the  new 
form  is  so  unlike  its  parent  that  it  is  regarded  as  a  new  species, 
often  termed  an  elementary  species.  The  new  forms  arising  in 
this  way  by  a  leap  or  bound  as  it  were  are  called  mutants.  The 
phenomenon  is  sometimes  spoken  of  as  discontinuous  variation  in 
contrast  with  fluctuating  variation.  Mutations  were  first  thor- 
oughly studied  by  De  Vries  in  one  of  the  evening  primroses 
((Enothera  lamarckiana),  which  may  be  taken  to  illustrate  this 
type  of  variation.  This  is  a  large  flowering  evening  primrose.  It 
is  supposed  to  have  been  native  to  North  America  since  speci- 
mens occur  in  several  herbaria  collected  in  some  of  the  southern 
states.  It  was  introduced  into  Europe  where  it  is  grown  in 
gardens,  and  as  an  escaped  plant  it  also  grows  wild  there  in  a 
number  of  places.  De  Vries  observed  it  growing  wild  near 
Amsterdam  in  Holland.  Growing  with  Lamarck's  evening  prim- 
rose ((Enothera  lamarckiana)  were  several  other  primroses  which 
could  be  recognized  as  different  because  of  the  form  of  the 


462 


GENERAL   MORPHOLOGY   OF  PLANTS 


rosettes.  These  were  different  from  any  known  species  of 
evening  primrose.  One  form  (O,  Icevifolia)  with  smooth  leaves 
was  found  growing  in  a  group  a  little  distance  from  the  main 
body  of  O.  lamarckiana,  where  it  was  reproducing  itself.  The 
different  forms  found  growing  wild  were  transplanted  to  the 


Fig.  414. 

Large  plant.  Lamarck's  primrose  (CEnothera  lamarckiana) ;  small  plant  at  the  right,  dwarf 
primrose  (CEnothera  nanella),  a  mutant  from  Lamarck's  primrose.     (After  MacDougall.) 


garden.  Seeds  from  O.  lamarckiana  were  sown  in  the  garden  in 
large  numbers.  Some  of  these  seeds  developed  forms  exactly 
like  those  new  ones  found  in  the  field.  After  several  years  of 
study  and  experimentation  several  distinct  mutants  of  O.  lamarck- 
iana were  obtained  in  pure  culture  in  the  garden,  which  were 
new  forms  or  elementary  species  as  they  are  called. 

When   close    pollinated    these    forms    bred  true,  except  that 
some  of  them  threw  off  mutants  also;  the  forms  thrown  off  by 


SOME  PRINCIPLES  OF  PLANT   EVOLUTION       463 

the  primary  mutants,  however,  were  not  new  forms.  Some  of 
them  were  the  original  parent,  while  others  were  one  or  more  of 
the  sister  species.  This  suggests  that  the  parent  form  possesses 
more  characters  than  it  can  give  expression  to  in  one  individual. 
Some  of  them  are  "  hidden  "  or  latent,  and  when  some  of  these 
latent  ones  express  themselves  they  do  so  at  the  expense  of  others 
which  in  turn  become  latent  or  hidden. 


CHAPTER   XLI. 
SOME  PRINCIPLES    OF    PLANT    BREEDING. 

648.  Object  of  plant  breeding. — Plant  breeding  has  for  its 
object  the  improvement  of  cultivated  varieties  of  plants,  the 
selection  and  improvement  of  promising  wild  plants,  and  the  pro- 
duction of  new  and  better  varieties.  Its  success  is  dependent  to 
some  extent  on  a  knowledge  of  the  laws  and  factors  of  evolution, 
as  well  as  on  an  intelligent  analysis  and  handling  of  the  materials. 
The  factors  are  the  same  as  those  operating  in  nature  on  wild 
plants,  but  in  many  points  artificial  methods  are  introduced  to 
replace  the  natural  methods  operating  in  the  world  at  large.  In 
this  way  progress  is  more  rapid  because  favorable  conditions  can 
be  provided,  a  better  food  supply  can  be  furnished,  competition 
can  be  removed,  variation  can  be  amplified,  and  an  intelligent 
selection  can  fix  upon  those  characters  of  greatest  value  for  the 
purpose  in  view,  and  quickly  eliminate  the  undesirable  forms. 
Two  principal  lines  of  plant  breeding  might  be  mentioned 
here. 

First,  the  improvement  of  existing  species  or  varieties  in  one  or 
several  directions,  in  order  to  obtain  the  highest  percentage  in 
content  of  certain  desirable  substances,  as  starch  content,  sugar 
content,  oil  content,  protein  content,  etc.  This  results  in  the 
production  of  what  are  called  races.  Such  races  can  only  be 
maintained  by  continued  selection  in  breeding,  otherwise  they 
rapidly  deteriorate. 

Second,  the  production  of  entirely  new  forms  of  plants,  in  the 
nature  of  varieties,  subvarieties,  subspecies,  or  physiological 
species,  forms  which  are  different  from  the  parent  by  the  posses- 
sion of  certain  characters  not  shown  by  the  parent. 


SOME  PRINCIPLES   OF   PLANT   BREEDING          46$ 

I.     THE    IMPROVEMENT    OF    EXISTING    VARIETIES. 

649.  Cultivated  races  of  plants.— Until  recent  years  plant 
breeders  have  given  their  attention  chiefly  to  the 'production  of 
varieties  which  differed  from  each  other  in  regard  to  form,  color, 
productivity,  etc.  In  recent  years  increasing  attention  has  been 
given  to  improving  existing  varieties  in  the  direction  of  increas- 
ing the  percentage  of  certain  constituent  substances  in  the  com- 
mercial plant  product.  For  example,  increase  in  the  percentage 
of  sugar  in  the  sugar  beet  and  sugar  cane;  increase  in  the  per- 
centage of  protein  in  corn  and  wheat,  of  oil  in  corn,  etc.  Since 
these  cannot  well  be  distinguished  as  varieties,  there  is  a  ten- 
dency to  apply  the  term  race  to  highly  developed  and  selected 
variations  of  this  kind.  There  are  great  variations  in  the  per- 
centages of  these  constituent  substances  in  plant  products.  By 
selecting  the  seed  (or  cuttings,  grafts,  etc.,  from  those  propa- 
gated by  asexual  methods)  from  individuals  of  a  good  variety 
which  yield  the  highest  percentage  in  the  desired  constituent  (of 
course  having  regard  to  the  proper  physical  conformation  of  the 
plant),  planting  this  and  selecting  again  from  the  individuals 
among  the  offspring  of  the  selected  ones,  and  repeating  this  for 
several  years,  a  high  standard  of  excellence  can  be  attained. 
With  these  races  the  process  of  selection  and  good  cultivation 
must  continue  year  after  year,  otherwise  deterioration  results. 
The  percentage  of  the  desired  constituent  is  determined  either  by 
chemical  or  physical  analysis. 

Seed  corn  (Indian  corn  or  maize)  can  be  selected  by  a  physi- 
cal analysis.  The  proportion  of  starch  in  the  grain  is  inverse  to 
the  proportion  of  gluten  or  the  size  of  the  embryo.  A  section  of 
the  grain  (paragraph  n  and  fig.  14)  will  show  to  the  eye  the 
proportion  of  these  constituents  to  each  other.  When  the  white 
starchy  portion  in  the  center  is  limited,  the  hard  outer  gluten- 
bearing  portion  will  be  greater.  If  one  is  selecting  for  protein 
content,  grains  are  chosen  which  have  a  small  starch  content, 
since  the  horny  layer  containing  gluten  (a  protein  substance)  and 
the  embryo  (containing  protein)  are  both  inverse  in  bulk  to  that 


466  GENERAL   MORPHOLOGY   OF   PLANTS 

of  the  starch.  Corn,  therefore,  can  be  selected  so  as  to  develop 
two  races,  one  for  protein  and  oil,  and  one  for  starch.  In 
Illinois,  where  a  great  deal  of  attention  is  given  to  breeding  corn, 
the  oil  content  has  been  raised  from  between  4-5  per  cent  to  7  per 
cent,  and  in  other  races  has  been  reduced  to  2  per  cent.  The  grains 
of  corn  on  a  single  ear  all  have  nearly  the  same  percentage  of  a 
given  constituent.  A  few  kernels  then  can  be  examined  on 
different  ears,  and  from  the  ear  giving  the  highest  percentage  of 
the  desired  constituent  the  remaining  kernels  can  be  planted. 
The  product  from  this  seed  can  be  subjected  to  a  similar 
selection,  and  so  on  each  year  until  the  high  standard  of  excel- 
lence or  the  desired  hereditary  percentage  is  reached.  The  ker- 
nels from  each  ear  are  sown  in  separate  rows  or  patches  so  that 
the  crop  from  the  different  ears  can  be  compared.  Thereafter 
the  process  must  be  continued  for  the  purpose  of  growing  seed 
in  order  to  keep  the  race  up  to  the  high  standard.  This  is  true 
in  all  selection  as  has  been  pointed  out  above.  At  this  point  seeds- 
men can  continue  the  selection  and  furnish  seed  to  the  growers, 
or  the  grower  can  each  year  raise  his  own  seed. 

A  race  of  corn  with  high  starch  content  is  better  for  feeding 
hogs,  since  a  firmer  and  better  quality  of  bacon  is  produced  than 
from  corn  with  a  high  oil  content.  Glucose  is  manufactured  from 
the  starch,  but  manufacturers  of  glucose  from  corn  prefer  a  corn 
having  a  high  percentage  of  protein  and  oil,  since  in  the  process  of 
separating  the  starch  from  the  kernels,  the  by-products,  protein 
and  oil  (from  the  horny  layer  and  embryo)  are  cheaply  obtained 
and  sold  for  a  good  price.  Therefore  they  wrould  be  glad  to  pay 
a  higher  price  for  a  race  of  corn  containing  a  high  percentage 
of  oil  and  protein  even  though  the  percentage  of  starch  were 
reduced.  A  company  which  manufactures  glucose  could  afford  to 
pay  five  cents  more  per  bushel  for  corn  containing  one  pound 
more  of  oil.  For  the  50,000,000  bushels  which  this  company  use 
annually  this  would  mean  $2,500,000  more  than  for  the  same 
amount  of  a  common  race  of  corn. 

650.  In  connection  with  breeding  for  these  constituents  corn 
should  be  bred  for  physical  perfection,  which  includes  length  and 


SOME   PRINCIPLES   OF   PLANT   BREEDING          46? 

circumference  of  ear,  shape  of  ear  and  cob,  number  of  kernels  in 
a  row  and  number  of  rows,  size  and  shape  of  kernels,  weight  and 
color  of  grain  and  cob.  White  corn  meal  is  preferred  by  some 
for  domestic  use  and  is  almost  exclusively  used  in  the  south; 
some  in  the  north  and  northwest  prefer  the  yellow  meal.  This 
preference  in  some  cases  is  probably  due  to  custom.  Attention 
should  also  be  given  to  developing  in  harmony  with  this  an  all 
round  good  plant,  and  to  yield  per  acre.  In  every  field  of  com- 
mon corn  there  are  stalks  which  do  not  bear  ripe  ears,  i.e.,  are 
"  barren."  These  often  produce  more  pollen  than  fertile  plants 
and  exercise  a  great  influence  in  pollinating  the  fertile  ears.  In 
selection  all  such  stalks  should  be  removed  before  the  pollen  ma- 
tures in  order  that  this  character  may  not  be  carried  over  into  the 
seed.  Races  are  bred  which  produce  a  single  large  ear  on  a  stalk. 
These  are  more  valuable  when  corn  is  husked  by  hand.  When 
it  is  husked  by  machinery  to  feed  to  cattle,  races  with  several 
small  ears  to  each  stalk  are  preferred.  Races  and  varieties  are 
also  bred  which  are  more  suitable  to  soil  or  climatic  conditions, 
and  varieties  have  been  developed  which  range  from  the  tropics 
to  the  Lake  Superior  region. 

651.  In  Minnesota  wheats   have   been  bred  to  increase  the 
number  of  bushels  per  acre,  the  famous  "  Minnesota  No.  169  " 
producing  three  to  five  bushels  more  per  acre  than  the  ordinary 
wheats.      When  grown  largely  over  the  state  it  showed  an  aver- 
age yield  of  18  per  cent  over  the  common  wheats.     The  gradual 
development   of    these    improved    races    of    different    cultivated 
plants  and  their  general  cultivation  in  place  of  the  common  sorts 
will  add  many  millions  of  dollars  to  the  value  of  our  crops  with 
no  additional  cost  in  the  production. 

II.    THE    PRODUCTION    OF    NEW   VARIETIES. 

652.  Variation  increased  by  cultivation,  by  better  food 
supply  and  by  crossing. — It  is  well  known  that  cultivation  and 
an  increased  food  supply  make  plants  more  variable  than  they 
are  in  the  wild  state.    The  plant  breeder  seizes  upon  this  and 


468  GENERAL   MORPHOLOGY   OF  PLANTS 

then  selects  the  most  promising  forms.  By  crossing  different 
varieties  with  the  promising  ones,  or  by  crossing  closely  related 
species  the  offspring  is  made  more  variable,  which  gives  a  wider 
range  to  select  from  and  makes  possible,  by  this  wider  range  of 
variation,  forms  which  are  more  productive  and  of  better  quality 
and  of  a  hardier  nature.  The  crossing  is  brought  about  by 
artificial  pollination  since  the  parents  can  be  selected  for  definite 
purposes,  one  parent  possessing  one  desirable  quality  and  the 
other  parent  another  desirable  quality,  with  the  result  that  these 
two  qualities  can  often  be  combined.  This  improved  form  can 
then  be  crossed  with  another  possessing  another  desirable  quality. 
The  hybrid  or  "  cross  "  is  often  crossed  again  with  one  of  its 
parents,  which  often  induces  greater  variability  and  also  often 
gives  greater  fertility.  This  furnishes  a  greater  number  of  varia- 
tions to  select  from. 

653.  Artificial  pollination. — The  artificial  pollination  is  ac- 
complished in  the  following  way.  Before  the  flower  is  open 
the  stamens  are  removed  from  one  parent,  and  if  the  stigma  of 
the  pistil  is  not  ready  for  the  reception  of  the  pollen  the  flowers 
are  covered  with  paper  bags  to  exclude  insects  which  might 
introduce  pollen  from  an  undesirable  parent.  One  must  be  sure 
that  the  stamens  are  removed  before  they  begin  shedding  their 
pollen.  The  pollen  is  sometimes  shed  before  the  flower  is  open. 
A  little  examination  of  a  few  flowers  will  show  when  the  opera- 
tion of  emasculation,  as  the  removal  of  the  stamens  is  called, 
should  be  performed.  Some  open  the  flower  and  with  forceps  or 
a  hook  pull  off  the  stamens,  but  a  better  method  practiced  by 
some  is  to  cut  away  the  calyx,  corolla  and  stamens  near  the 
receptacle  with  a  small  pair  of  scissors.  The  emasculated  flower 
is  then  covered  with  a  paper  bag  which  is  gathered  and  tied 
closely  to  the  branch  at  the  neck  in  order  to  shut  out  insects, 
until  the  stigma  reaches  the  receptive  stage,  or  until  the  pollen  is 
ready.  When  the  pollen  is  ripe  it  is  gathered  in  a  small  recep- 
tacle. If  one  wishes  to  be  very  careful  to  have  the  pollen  free 
from  that  of  other  individuals  or  variety,  as  is  necessary  in  care- 
ful experimental  work,  the  male  flower  should  be  covered  with  a 


SOME  PRINCIPLES  OF  PLANT   BREEDING         469 

paper  bag  before  it  opens.  The  pollen  is  applied  in  various 
ways  according  to  the  necessities  of  the  case.  In  large  opera- 
tions it  is  often  applied  by  the  fingers.  In  other  cases  with  a 
camel's-hair  brush,  but  this  is  objectionable  in  smaller  operations 
and  where  one  is  pollinating  several  different  varieties,  for  there  is 
danger  of  pollen  adhering  to  the  brush  when  the  next  variety  is 
taken  up.  Some  use  a  pointed  scalpel  made  by  inserting  the 
head  of  a  pin  in  a  small  stick  and  pounding  the  pointed  end 
into  a  thin  blade.  After  the  pollen  is  applied  to  the  stigma  the 
flower  is  again  covered  with  the  paper  bag,  until  the  receptive 
stage  of  the  stigma  is  passed.  In  some  cases  bags  of  gauze  are 
used  which  exclude  the  insects,  and  in  case  the  fruit  or  seed  is 
large  enough  it  is  caught  and  saved,  in  case,  at  maturity,  the 
fruit  or  seed  should  fall  before  being  harvested  by  hand.  In 
some  cases  thousands  of  these  seeds  are  obtained  and  planted  in 
order  to  have  as  wide  a  range  of  variation  as  possible  to  select 
from. 

654.  Selection  in  plant  breeding. — Artificial  selection,  that 
is  selection  by  man,  here  merely  replaces  natural  selection. 
Plant  breeding  by  artificial  selection  has  long  been  practiced  by 
man,  so  long  that  we  do  not  even  know  the  origin  of  some  of  our 
most  important  domesticated  plants  to  say  nothing  of  the  early 
history  of  their  development  and  improvement.  The  practice 
began  with  man  in  his  savage  state.  It  is  only  during  recent 
years  that  civilized  man  has  kept  any  record  of  the  origin  of  new 
forms,  and  many  of  these  have  so  far  departed  from  any  feral 
species  at  present  known  that  we  cannot  now  trace  the  history, 
nor  in  some  cases  determine  what  species  might  have  been 
the  parent  of  the  form  now  in  cultivation.  The  origin  of  some 
is  known  while  that  of  others  is  a  matter  of  conjecture. 
The  origin  of  many  of  the  more  recent  introductions  is  com- 
paratively well  known,  and  the  pedigree  of  some  has  been  quite 
accurately  kept.  As  soon  as  savage  man  began  to  apply  the 
principle  of  selection  and  cultivation  even  on  a  crude  scale, 
the  fruits,  grains  and  vegetables  which  formerly  he  collected 
from  feral  plants  became  more  productive,  larger  and  of  better 


4/0  GENERAL   MORPHOLOGY   OF  PLANTS 

quality.  Experience  and  a  growing  insight  into  the  laws  of  evo- 
lution brought  vastly  improved  methods,  until  now  wonderful 
results  are  obtained.  The  science  of  plant  breeding  is  still  much 
of  it  in  an  experimental  stage,  but  in  some  directions  definite  ends 
can  be  planned  and  worked  for  with  more  or  less  certainty  of 
success,  though  in  a  majority  of  cases  the  length  of  time  needed 
to  attain  the  desired  result  and  the  degree  of  success  remains, 
and  will  probably  always  remain,  an  unknowrn  quantity.  Studies 
of  experimental  evolution  will  make  the  way  more  and  more 
clear  in  the  future,  just  as  the  increased  knowledge  of  the  laws  of 
variation,  adaptation,  heredity,  etc.,  gives  plant  breeders  to-day 
greater  success  than  was  ever  attained  before. 

655.  Severity  in  selection. — From  the  many  thousands  a 
few,  the  most  promising,  are  selected.  This  weeding-out  process 
of  the  undesirable  forms,  or  "  rogues  "  as  they  are  termed,  is 
often  called  "  rogueing."  The  thousands  of  plants  which  some 
plant  breeders  discard,  in  order  to  select  only  the  very  few  of  the 
highest  quality,  sometimes  seems  like  ruthless  destruction,  but  it 
is  this  rigorous  system  of  selection  which  brings  the  highest 
success.  One  might  paraphrase  the  old  adage  of  "  spare  the  rod 
and  spoil  the  child  "  by  saying,  "  spare  the  rogue  and  spoil  the 
breed,"  The  flowers  from  the  offspring  of  these  selected  hybrids 
are  protected  from  cross  pollination,  and  seeds  are  again  planted 
until  the  desired  quality  in  fruit  (color,  flavor,  size,  period  of 
maturity,  shipping  quality,  vigor,  hardiness,  etc.)  is  obtained. 
In  the  case  of  plants  which  require  several  years  of  growth  from 
the  seed  before  fruit  and  seed  is  obtained  (as  in  the  case  of  apples, 
pears,  peaches,  plums,  etc.),  the  time  of  the  experiment  can  be 
shortened  by  grafting  the  seedling  shoot  on  a  mature  stock.  If 
the  fruit  is  not  satisfactory  in  all  respects  the  process  must  be 
continued.  When  the  desired  results  are  obtained  it  is  then 
necessary  to  fix  the  variety.  When  the  variety  can  only  be 
propagated  by  seed  this  must  be  done  by  continued  selection. 
Some  varieties  will  remain  quite  constant  from  the  seed  from  the 
first,  and  it  is  then  only  necessary  to  continue  good  cultivation  and 
selection  of  seed  from  the  most  productive  plants  which  have  the 


SOME  PRINCIPLES  OF  PLANT  BREEDING          4?  I 

other  desirable  qualities.     The  cereals  for  example  must  be  prop- 
agated from  the  seed. 

656.  Selection  and  fixing  of  varieties  for  special  pur- 
poses.— Varieties  are  selected  and  propagated  for  various  pur- 
poses, as  for  color  of  flour,  high  percentage  of  gluten,  or  oil,  or 
starch,  etc.  Sugar  beets  are  selected  for  productivity  and  high 
percentage  of  sugar.  It  is  noteworthy  that  in  all  cases  when  a 
variety  has  been  bred  to  a  high  state  of  excellence,  continued 
selection  of  seed  from  the  best  must  be  followed  up  continuously, 
otherwise  the  variety  will  deteriorate,  since  even  with  the  best  and 
most  highly  bred  varieties  variation  continues.  The  variety  is 
not  fixed  by  selection  so  that  it  cannot  change.  By  selection 
man  can  intensify  the  desired  character  and  increase  the  fre- 
quency with  which  it  occurs.  He  can  do  no  more.  If  selection 
were  not  continued,  the  varieties  would  gradually  deteriorate 
since  in  the  case  of  those  where  cross  pollination  took  place  the 
variety  would  gradually  sink  to  the  level  of  the  average.  This 
average  would  give  varieties  still  lower  than  the  lowest  of  the 
highly  bred  variety  which  would  tend  to  a  still  lower  average 
level.  The  same  result  would  also  finally  be  reached  in  the  case 
of  those  varieties  which  were  self-pollinated  if  selection  were  not 
continued.  Selection  should  also  be  made  in  the  light  of  corre- 
lated variation.  For  example,  the  selection  of  the  largest  ears  of 
corn  which  could  be  found  in  a  field  would  not  necessarily  give 
the  best  results.  The  largest  ears  borne  on  the  best  stalks,  and  in 
some  cases  on  stalks  where  there  is  more  than  one  ear,  give  better 
results;  also  ears  with  the  highest  percentage  of  grain  in  pro- 
portion to  cob.  But  recent  experiments  show  that  the  best 
method  is  selection  from  an  area  which  gives  the  highest  yield 
per  acre.  In  the  case  of  plants  which  can  be  propagated  asex- 
ually,  variation  in  the  desired  variety  can  be  lessened  and  the 
character  more  permanently  fixed  by  asexual  methods  of  propa- 
gation,* as  by  grafting  in  the  case  of  apples,  pears,  etc.,  by 

*  This  is  sometimes  called  asexual  multiplication  of  extremes.  When  a 
variety  from  which  it  is  desired  to  select  has  reached  a  high  state  of  fluctua- 
ting variation,  it  is  the  extremes  of  variation  which  are  selected,  and  usually 


472  GENERAL   MORPHOLOGY   OF   PLANTS 

budding  as  in  the  peach,  by  layering  as  in  the  case  of  rasp- 
berries and  blackberries,  by  offsets  as  in  the  case  of  strawberries, 
etc.,  or  by  root  stocks,  tubers,  bulbs,  etc.,  in  the  case  of  many 
other  plants. 

657.  Difficulty  sometimes  encountered  in  fixing  desirable 
varieties. — It  sometimes  happens  as  a  result  of  crossing  that  the 
resulting  hybrids  and  their  progeny  are  so  variable  and  continue 
to  be  so  that  no  desirable  type  or  variety  can  be  fixed.     It  runs 
out  or  changes  in  each  succeeding  generation.     This  is  especially 
the  case  in  certain  crosses  of  squashes,  as  Bailey  has  shown.     In 
a  cross  between  a  summer  yellow  crook-neck  and  a  white  bush 
scallop,  a  squash  of  great  excellence  was  obtained  which  com- 
bined the  merits  of  summer  and  winter  squashes,  attractive  in 
form,  habit,  size  and  color.     It  was  a  most  promising  type.     The 
seeds  of  the  finest  squash  in  this  plant  were  saved  and  planted. 
Only  two  or  three  plants  from  this  seed  were  almost  like  the 
parent,  the  rest  being  very  different,  altogether  there  being  one 
hundred  and  ten  different  kinds  "  distinct  enough  to  be  named 
and  recognized."     The  flowers  of  one  of  these  plants  were  infertile 
to  their  own  pollen,  and  as  the  plants  were  slightly  different,  cross 
pollination  was  resorted  to.     A  few  fruits  were  developed  and  the 
seeds  of  these  were  planted  the  following  year.     "  Not  one  seed 
produced  a  squash  like  the  parent." 

658.  Objects  in  developing  new  varieties. — There  are  many 
useful  ends  toward  which  the  plant  breeder  works.     Some  of 
these    have    already    been    mentioned    as    greater    productivity, 
increase  of  the  desired  product  as  percentage  of  flour,  gluten, 
oil,  starch,  etc. ;    in  fruits,  improvement  of  flavor,  color,  texture, 
varieties  for  home  consumption,  for  keeping  or  shipping  quali- 
ties, etc. ;    in  fibers,  length,  strength,  fineness  or  coarseness.     So 
there  is  the  development  of  varieties  suited  to  different  climates. 

the  best  extreme,  since  that  possesses  the  highest  standard  of  the  desired 
quality.  Sometimes,  however,  there  may  be  an  undesirable  quality  which 
must  be  gotten  rid  of  or  decreased.  Selection  proceeds  then  to  develop 
a  high  standard  of  extremes  in  desirable  qualities  and  a  low  standard  of 
extremes  in  the  undesirable  qualities  if  they  cannot  be  entirely  gotten  rid  of. 


SOME  PRINCIPLES  OF  PLANT  BREEDING         473 

Indian  corn  is  a  good  example  of  this.  Originally  a  subtropical 
plant  it  is  now  cultivated  over  a  wide  range  of  the  north  temper- 
ate zone,  with  varieties  of  low  stature  which  mature  in  six  to 
eight  weeks  in  the  northern  latitudes.  A  very  important  object 
in  plant  breeding,  and  one  which  should  not  be  overlooked,  is  the 
harmonious  development  of  all  parts,  the  general  form  and  con- 
stitution of  the  plant,  in  order  that  these  auxiliary  characters 
which  contribute  to  the  well  being  of  the  plant  as  a  whole,  which 
bring  the  greatest  returns  in  proportion  to  the  cost  of  production, 
as  ease  of  cultivation  and  handling,  conformity  to  soil  and  cli- 
matic conditions,  resistance  to  disease,  etc.,  may  be  present. 
Breeding  for  varieties  which  are  resistant  to  disease  is  one  of  the 
most  recent  efforts  of  the  plant  breeder.  Its  success  is  based  on 
the  same  natural  laws  which  make  possible  the  improvement  of 
varieties  in  many  other  directions,  viz.,  variation  and  selection. 
Plants  vary  in  their  disease-resisting  qualities  just  as  animals  do. 
It  is  rare  that  one  finds  all  of  the  plants  in  a  given  locality  equally 
subject  to  a  fungus  disease.  The  resistant  individuals  are 
selected  to  propagate  from,  either  by  seed  or  by  asexual  means 
according  to  the  case  in  hand.  This  process  of  selection  is  con- 
tinued for  several  years,  weeding  out  those  which  are  susceptible 
to  attack  until  resistant  varieties  are  obtained.  Some  success 
has  already  been  obtained  in  this  direction  in  the  case  of  rust-* 
resisting  varieties  of  wheat,  and  in  varieties  of  cotton,  clover,  etc., 
which  are  resistant  to  certain  of  the  diseases  common  to  them. 
It  is  not  to  be  expected  that  complete  resistance  to  disease  in 
plants  will  be  attained  by  plant  breeding  of  disease-resistant  varie- 
ties, because  variation  cannot  be  eliminated.  Some  individuals 
will  be  more  susceptible  than  others  and  will  now  and  then 
become  diseased,  the  percentage  varying  with  the  variations  in 
external  and  cultural  conditions  as  well  as  with  the  persistence 
and  intelligence  with  which  the  selection  is  continued.  Disease- 
resistant  varieties,  like  other  varieties,  depend  on  continued  selec- 
tion for  the  maintenance  of  a  high  standard  of  excellence. 

659.   "  Breaking  the  type  "  in  plant  breeding. — When  the 
plant  breeder  undertakes  to  improve  a  variety,  or  develop  new 


474  GENERAL   MORPHOLOGY   OF   PLANTS 

ones,  if  it  does  not  already  present  great  variation  among  the 
individuals  it  is  necessary  to  bring  it  into  a  variable  state.  The 
plant  may  vary  only  with  reference  to  percentages  of  a  desirable 
quality  of  product.  In  this  case  continued  selection  would  only 
maintain  a  high  degree  of  excellence  in  this  respect.  It  may  be 
desirable  to  develop  a  different  variety  which  may  possess  this 
same  quality  in  a  higher  state  of  excellence  or  to  work  for  new 
qualities.  If  the  variety  to  be  experimented  on  is  a  comparatively 
stable  type  it  is  first  necessary  to  get  it  out  of  this  state  of  sta- 
bility, otherwise  no  satisfactory  improvement  could  be  made.  It 
is  necessary  to  "  break  the  type,"  as  plant  breeders  say.  This 
may  be  done  in  one  of  several  ways  according  to  conditions. 
Methods  much  employed  are:  first,  by  cross  pollination  of 
closely  related  varieties ;  second,  by  cross  pollination  of  a  variety 
with  its  species;  third,  by  cross  pollination  of  closely  related 
species.  The  hybrids  from  these  crosses  are  likely  to  show 
greater  variation  than  either  of  the  parent  forms.  The  type  may 
often  be  still  farther  broken,  or  greater  variation  may  often  be 
induced,  fourth,  by  crossing  the  hybrid  with  one  or  both  of  its 
parents.  Variation  is  resorted  to  because  the  greater  the  range  of 
variation  the  greater  chance  there  is  of  obtaining  the  desired 
qualities  among  the  individuals.  Variation  can  also  be  induced 
in  other  ways.  It  is  well  known  that  when  feral  plants  are  taken 
into  cultivation  and  given  better  food,  and  competition  is  largely 
removed,  the  plants  tend  to  vary,  and  often  this  variation  extends 
over  a  wide  range.  So  when  plants  are  introduced  in  new 
localities  where  the  conditions  are  different,  variation  often  is  the 
result.  This  fact  is  often  taken  advantage  of  and  leads  to  a  fifth 
principle  according  to  which  the  type  can  be  broken,  namely,  by 
securing  seed  from  a  different  locality.  This  seed  from  a  distant 
locality  when  planted  side  by  side  with  seed  of  plants  which  in 
their  own  locality  are  quite  stable  and  show  little  variation,  often 
produces  plants  which  are  very  variable  and  thus  affords  a  wide 
range  for  the  selection  of  varieties  which  can  be  still  farther 
improved  by  selection.  This  is  often  combined  with  a  sixth 
method,  that  of  crossing  individuals  of  the  same  variety  which 


SOME  PRINCIPLES  OF  PLANT  BREEDING  4?$ 

come  from  widely  different  localities.  For  example,  seed  of 
a  given  variety  obtained  from  a  distant  locality  is  planted 
in  a  given  locality  where  the  same  variety  is  stable.  The 
breeder  cross-pollinates  these  with  the  individuals  of  the  same 
variety  in  his  own  locality,  which  is  apt  to  induce  still  greater 
variation. 

660.  A  definite   purpose   in   crossing. — The  plant  breeder 
usually  works  for  a  definite  purpose  in  view.     Sometimes  it  is 
possible  to  predict  results,  i.e.,  to  form  an  idea,  or  a  picture,  several 
years  in  advance,  of  the  shape  and  quality  of  the  plant  product 
desired.     For    example,    seedsmen    have    on    several    occasions 
described  to  plant  breeders  the  character  and  quality  of  a  wholly 
new  variety  of  beans  which  they  believed  would  possess  especial 
commercial  merit.     The  plant  breeder  was  asked  how  long  it 
would  take  to  breed  this  variety,  and  being  told  that  it  could  be 
produced  in  about  three  years,  the  seedsman  advertised  the  seed 
in  advance  of  the  existence  of  the  variety.     It  is  rare,  however, 
that  the  breeder  can  work  with  such  precision  as  to  determine 
the  time  at  which  the  desired  result  can  be  obtained  except  in 
dealing  with  varieties  whose  variations  in  different  directions  are 
already  known  to  him,  and  by  knowing  the  variations  and  plas- 
ticity of  his  material  he  can  select  during  several  years  for  this 
one  result. 

661.  Work  for  one  thing  at  a  time. — The  experience  of  most 
breeders  leads  them  to  work  for  one  thing  at  a  time,  since  if  the 
breeder  selects  his  plants  for  several  qualities,  progress  towards 
excellence  in  one  direction  is  impeded  and  often  defeated  because 
of  some  antagonism  in  the  strain  he  is  working  on  between  some 
of  the   qualities  he   is  striving  to   develop.     When  the  desired 
excellence  is  reached  in  regard  to  one  quality,  plants  possessing 
this  quality  are  then  bred  for  another  quality.     If  certain  of  the 
desired  qualities  cannot  be  obtained  from  this  variety  by  selec- 
tion, it  is  then  crossed  with  some  closely  related  variety  possessing 
this  character  and  selection  is  again  resorted  to  until  the  plant 
and  productivity  as  a  whole  has  been  brought  to  the  highest  state 
of  excellence,  or  the  state  of  excellence  desired.     Selection  may  be 


4/6  GENERAL   MORPHOLOGY   OF  PLANTS 

carried  too  far  in  certain  directions,  when  it  will  be  necessary  to 
breed  back  to  the  best  state,  as  was  the  case  with  a  variety  of 
walnuts  bred  by  Burbank.  He  was  breeding  for  a  nut  with  a 
thin  shell.  He  succeeded  so  far  as  to  produce  a  nut  with  a  shell 
so  thin  that  the  birds  could  break  through  it  and  eat  the  meat. 
It  was  then  necessary  to  breed  back  a  thicker  shell,  at  the  same 
time  retaining  the  other  good  qualities  of  the  nut  and  the  general 
vigor  of  the  tree. 

662.  Crossing  different  species  for  the  production  of  new 
varieties. — Where  species  not  too  distantly  related  possess  cer- 
tain characters  which  it  is  desired  to  bring  into  one  variety,  they 
are  often  crossed  for  this  purpose  with  excellent  results,  but  some 
plant  breeders  advise  against  the  crossing  of  species  as  a  rule. 
Some  of  the  reasons  for  not  crossing  species  are  that  the  hybrids 
of  species  are  apt  to  be  sterile  or  at  least  to  possess  a  high  per- 
centage   of    sterility.     The    more    distantly   related    the    species 
crossed,  the  greater,  in  general,  will  be  the  percentage  of  sterility. 
Thus  little  or  no  seed  is  obtained  which  makes  the  propagation  of 
the  new  variety  unprofitable  if  it  is  to  be  propagated  from  the 
seed.      If  a  valuable  variety  is  obtained  in  this  way  which  has 
a  low  percentage  of  fertility,  the  percentage  of  fertility  can  often 
be   improved  by  crossing  the   hybrid  with  one  of  its   parents. 
On  the  other   hand   hybrids  of  varieties  are   apt  to  possess   a 
high  percentage    of    fertility.      Crossing  of   species,   if  they  are 
not  closely  related,  is  apt  to  be  more   or  less  guess  work,-  and 
in  the  large  number  of  cases  does  not  lead  to  success.      Now 
and   then,  however,  very  valuable  varieties  are  obtained  in  this 
way. 

663.  Relation    of   Mendel's    law    to    plant   breeding.*— 
Because  of  the  approximate  precision  with  which  the  hybrids, 
which  follow  Mendel's  law,  come  out  with  dominant  and  recessive 
characters,  it  has  been  thought  by  some  it  would  be  possible  to 
predict  the  nature  of  varieties  or  hybrids  which  one  could  obtain 
by  the  crossing  of  closely  related  species  or  varieties.     In  cross- 
ing varieties  differing  in  respect  only  to  one  character,  which 

*  For  special  assignment. 


SOME  PRINCIPLES  OF  PLANT   BREEDING  477 

hybridize  according  to  Mendel's  law,  nothing  would  be  gained 
because  only  two  forms  are  obtained,  which  are  exactly  like  the 
parents  (paragraph  646).  These  are  called  monohybrids.  In 
crossing  varieties  which  differ  in  respect  to  two  characters  which 
behave  according  to  Mendel's  law,  dihybrids  are  produced  and 
four  combinations  are  possible,  resulting  in  successive  genera- 
tions in  four  different  varieties  which  breed  true,  two  of  them 
like  the  parents  and  two  new  varieties.  For  example,  in  crossing 
the  blue-flowered  thorn  apple,  or  jimson  weed,  with  the  white- 
flowered  smooth  one,  besides  the  two  parent  forms,  two  new  ones 
are  obtained,  a  blue-flowered  smooth  one  and  a  white-flowered 
thorny  one.  So  in  the  case  of  three  different  unit  characters  in 
the  parents  eight  combinations  are  possible,  two  of  them  like 
the  parent  and  six  new  ones.  In  these  cases  it  is  possible  to 
predict  in  advance  the  new  forms  which  can  be  obtained  and 
selection  can  be  made  from  them. 

Very  important  results  have  in  fact  been  obtained  recently  by 
Biffen  of  Cambridge  University  in  England.  The  wheat  com- 
monly grown  in  England  is  a  soft  wheat,  i.e.,  with  a  high  per- 
centage of  starch  and  low  protein  content,  but  it  also  produces  a 
large  yield.  He  worked  to  develop  a  variety  of  wheat  having  a 
high  protein  content,  with  the  high  productivity  of  the  English 
wheat,  and  also  which  would  be  free  from  the  disease  known  as 
rust.  He  found  by  experimental  work  that  these  and  some  other 
characters  behaved  as  unit  characters  in  Mendelian  fashion  (par- 
agraph 646),  as  follows: 

Having  cropping  quality  dominant  to  poor  cropping  quality. 
Glutinous  wheat  (high  per  cent  protein)  dominant  to  starchy  wheat. 
Rusty  plants  'dominant  to  resistant  plants. 
Early  wheat  dominant  to  late. 
Red  grain  dominant  to  white. 
Rough  chaff  dominant  to  smooth. 
Bearded  wheat  dominant  to  bald. 
Stiff  stems  dominant  to  weak. 

By  crossing  in  various  combinations  he  was  able  to  produce 
a  variety  of  wheat  possessing  the  heavy  cropping  qualities  and 


4/8  GENERAL   MORPHOLOGY   OF   PLANTS 

good  straw  of  the  English  wheat,  the  high  protein  content  of  a 
foreign  wheat,  and  resistance  to  the  rust.* 

664.  Varieties  are  continually  changing. — It  is  a  matter  of 
common  observation  on  the  part  of  horticulturists  and  others  that 
many  of  the  new  varieties  put  upon  the  market  in  a  few  years 
are  so  greatly  changed,  that  they  no  longer  resemble  the  variety 
as  it  was  originally  known  and  described.     In  fact  several  differ- 
ent new  varieties  may  arise  from  it  in  different  sections  of  the 
country  without  any  effort  on  the  part  of  the  cultivators  to  de- 
velop them,  and  still  they  may  all  go  by  the  name  of  the  original 
new  variety.     This  is  due  to  several  causes.     First,  the  variety, 
although  in  general  breeding  true,  is  variable.     Second,  when  cul- 
tivated in  different  localities  where  climatic,  soil  and  food  con- 
ditions are  different,  variations  are  introduced  in  different  direc- 
tions.    Third,  the  growers,  while  not  attempting  to  breed  new 
varieties,  unconsciously  pursue  a  method  which  would  lead  to 
the  production  of  new  varieties.     In  the  selection  of  seed  it  is 
taken  from  the  best  plants  or  from  the  best  fruit.     Naturally  the 
ideals  of  different  persons  would  be  different  and  so  their  selection 
would  lead  in  the  direction  of  forming  new  variations  in  a  few 
years. 

665.  Records. — It    is   very   important    that   one    engaged  in 
plant  breeding  should  keep  a  careful  and  accurate  record  of  their 
work  so  that  the  pedigree  of  the  races  and  varieties  may  be  well 
known.      For  methods  of  keeping  records  reference  should  be 
made  to  some  work  on  plant  breeding  (see  Bailey's  Plant  Breed- 
ing, 4th  edition,  1906). 

NOTE.  —  The  plant  breeding  by  the  United  States  Department  of  Agricul- 
ture is  concerned  with  the  improvement  of  the  cotton  staple,  citrous  fruits, 
apples,  pineapples,  oats,  tobacco,  etc. 

*  See  Punnet,  R.  C.,  Applied  Heredity,  Harper's  Monthly,  December, 
1908. 


INDEX 


Abies  balsamifera,  rust  of,  280. 

Absorption,  33-36. 

Accessory  fruits,  188,  195. 

Acer  nigrum,  412. 

Acer  saccharinum,  412. 

Acer  saccharum,  412. 

Aceraceae,  412. 

Acorn,  189. 

Adansonia,  442. 

Adiantum    concinnum,    sperms    of, 

336;  embryo  of,  338. 
Adiantum   cuneatum,   egg  case  of, 

337- 

^cidia,  280-282. 
^cidiospores,  281,  289. 
/Ecidium  corruscans,  280. 
/Ecidium  esculentum,  280. 
Aerial  roots,  28,  40. 
Aerobes,  114. 
Aerobic  respiration,  114. 
Agar-agar,  243. 
Agaricus  campestris,  291-295. 
Agave  elongata,  405. 
Aggregate  fruits,  188,  192-194. 
Air,  purity  of,  116. 
Akene,  188,  202. 
Albugo  Candida,  258. 
Albuminous  seeds,  186,  385. 
Aleurone,  14,  15,  18. 
Alfalfa,  410. 

Alga-like  fungi,  247,  301. 
Algae,  211-243. 
Algae,  green,  212;   blue  green,  231; 

brown,  235;  red,  239. 
Almond,  192,  408. 
Alpine  grasses,  450. 
Alpine  shrubs,  450. 
Alternation  of  generations,  315,  324. 
Amanita  caesarea,  292. 
Amanita  mappa,  295,  296. 
Amanita  muscaria,  291,  296. 
Amanita  phalloides,  295. 
Amanita  verna,  296. 
Ament-bearing  plants,  403. 


Ammonia,  120. 

Ammonia  compounds,  119. 

Amoeba,  215. 

Ampelopsis  quinquefolia,  41. 

Anabaena,  233. 

Anabolism,  106. 

Anaerobes,  113,  114,  138. 

Anaerobic  respiration,  114. 

Ananas  sativa,  400. 

Anemophilous  flowers,  108,  171. 

Angiospermae,  210,  357,  375. 

Angiosperms,  207,  357,  375-391- 

Angiosperms,  review  of  characters, 

386. 

Animal  diastase,  134. 
Animal  respiration,  in. 
Annuals,  37. 

Annulus  of  mushrooms.  293,  294. 
Anther,  143;  versatile,  146;  introrse, 

146;  incumbent,  146;  adnate,  143; 

filament,  143;  lobes,  150. 
Antheridiophores,  306. 
Antheridium,     222-228,     230,     237, 

238,  240,  255,  304,  319,  335,  379, 

380. 

Anthoceros,  3I3~3I5,  351- 
An thocero tales,  315. 
Anthocerotes,  210,  314. 
Antipodal  cells,  382,  384. 
Antitoxin,  137,  138. 
Apogamy,  340. 
Apospory,  340. 
Apothecium,  262,  272. 
Apple  family,  406. 
Apple  leaf,  71. 
Apple  seed,  n. 
Apples,  407. 
Apricots,  408. 

Aquatic  plant  societies,  454. 
Arbutus,  415. 
Arceuthobium,  128. 
Archegoniophore,  309. 
Archegonium,   304,   308,   310,   317, 

319,  335,  336,  380. 


479 


48  o 


INDEX 


Archil,  275. 

Arctic-alpine  societies,  449. 

Arctium  lappa,  202. 

Aril,  197,  386. 

Arisaema  triphyllum,  163-165. 

Artichoke,  globe,  420. 

Artocarpus  incisa,  406. 

Arundinaria  macrosperma,  399. 

Asclepias,  75. 

Ascocarp,  262. 

Ascoma,  267,  272. 

Ascomycetes,  209,  248,  261-275,  301. 

Ascospores,  262,  263,  266. 

Ascus,  247. 

Ascus  fungi,  261-275. 

Asexual  reproduction,  223,  225,  237, 

239,  249,  255,  257. 
Ash,  416. 

Aspergillus  oryzae,  125,  134. 
Aspidium  acrostichoides,  329,  330. 
Asplenium  bulbiferum,  328. 
Assimilation,  90,  101,  105,  107,  121- 

123. 

Assimilation,  chemosynthetic,  106. 
Assimilation,  photosynthetic,   106. 
Assimilation,  synthetic,  106. 
Aster,  419. 
Auxospore,  235. 
Avena  sativa,  395. 
Azaleas,  415. 


Bacillariales,  209,  234. 
Bacillus,  135,  244. 
Bacillus  acidi  lacti,  134. 
Bacillus  diphtheriae,  137. 
Bacillus  subtilis,  135. 
Bacillus  tetani,  135,  136. 
Bacillus  tuberculosus,  137. 
Bacillus  typhosus,  136,  137. 
Bacteria,    103,    114,    118,    121-123, 

126,  132-139,  209,  244,  245. 
Bacteria,  diseases  caused  by,  136- 

I39-. 

Bacteria,  nutrition  of,  136. 
Bacterium,  135. 
Bacteroids,  122. 
Bamboo,  399. 
Bambusa  vulgaris,  399. 
Banana,  402. 
Banyan  tree,  29. 
Barberry,  87. 

Barium  carbonate,  108,  109. 
Barium  hydrate,  108-111. 


Barley,  396. 

Barley  smut,  277. 

Barriers  to  plant  migration,  437. 

Baryta  water,  109,  no. 

Basidiomycetes,  209,  276-303. 

Basidium  fungi,  276-303. 

Bassweeds,  228. 

Bass-wood,  413. 

Bast  portion  of  vascular  bundle,  31, 

53-58. 

Batrachospermum,  240,  242. 
Bean,  1-4,  7,  11. 
Bean,  castor,  or  castor  oil,  4-6. 
Bean,  scarlet  runner,  4. 
Beech  leaf,  71. 
Beech  order,  403. 
Beechnut,  190. 
Beet,  43-. 
Beggar  ticks,  202. 
Beggiatoa,  135,  245. 
Berry,  194. 
Bidens,  202. 
Biennials,  37. 
Bilabiate,  149. 
Biotic  factors,  424. 
Bird's-eye  maple,  412. 
Black  fungi,  265. 
Black  knot  of  plum,  265,  266. 
Black  rust  of  wheat,  284. 
Blackberries,  42,  192-195,  202,  406. 
Blade  of  leaf,  70. 
Blastophaga,  pollination  by,  180. 
Blue-green  algae,  231,  245. 
Bcehmeria  nivea,  405. 
Boletus  edulis,  297. 
Bracing  roots,  29. 
Bracken  fern,  330. 
Bracket  fungi,  292,  296-298. 
Bread  fruit,  406. 
Bread  mold,  248-251. 
Bromeliaceae,  401. 
Broom  corn,  398,  399. 
Brown  algae,  235-239;  uses  of,  239. 
Bryales,  323. 
Bryophyta,  207,  210. 
Bryophytes,  207. 
Bud  shoots,  39,  61-69. 
Buds,  adventitious,  45,  47. 
Buds,  axillary,  47. 
Buds,  characters  of,  63. 
Buds,  protection,  47,  48,  61-69. 
Buds,  respiration  of,  in. 
Buds,  terminal,  47. 
Buds,  winter  condition  of,  61-69. 


INDEX 


481 


Bulbils  of  club  moss,  346;  of  ferns, 

328. 

Bulbs,  43. 

Burdock,  seed  dispersal,  202. 
Butter  and  eggs,  148,  149. 
Buttercup,  142-144,  187,  189. 
Butternut,  buds  and  shoots  of,  66, 

67;  fruit,  190. 

Cacao,  414. 

Cacti,  45,  427,  447- 

Caesar's  agaric,  292. 

Catamites,  354,  355. 

Calcium,  117,  118. 

Calcium  carbonate,  109. 

Calla  lily,  165. 

Callithamnion,  242. 

Calluna,  273. 

Calyptra,  310,  322,  337,  338. 

Calyx,  142,  145,  149,  150,  154. 

Cambium,  53,  57~59,  I3I- 

Campanula,  pollination  of,  175,  176. 

Campanulales,  418. 

Camptosorus  rhizophyllus,  327. 

Cane  sugar,  18,  19. 

Cannabis  sativa,  402,  404. 

Cantaloupes,  419. 

Caprification,  181. 

Caprifig,  1 80. 

Capsule,  191;  syncarpous,  191. 

Capsule,  of  liverworts,  309,  311,  314; 

capsule  bearer,  309. 
Capsule  of  mosses,  320-322. 
Carbohydrates,  102,  104,  106,  126, 

130,  J33,  !34- 
Carbon,  15,  98-116. 
Carbon  dioxide,  98-116. 
Carbonate  of  lime,  109. 
Carbonic  acid,  101. 
Carduus,  419. 

Carboniferous  Age,  landscape  of ,  355. 
Carnation  rust,  129. 
Carnivorous  animals,  119. 
Carpel,  148,  379. 
Carpogonium,  240,  263. 
Carpospores,  239,  242. 
Carrot,  26,  43,  86. 
Caruncle,  4. 
Caryopsis,  189. 
Cassiope  tetragona,  88. 
Castor  bean,  4-6,  13. 
Catkins,  402. 
Caulicle,  8. 
Causes  of  plant  migration,  432,  434. 


Caustic  potash,  no. 

Cedar,  196,  202. 

Cedar  apples,  287,  288. 

Cedar  rust,  287,  288. 

Celery,  52. 

Cell  sap,  34,  213,  214. 

Cell,  structure  of,  in  Spirogyra,  213; 

plasmolysis  of.  214. 
Cellulose,  n,  17,  132. 
Central  cell,  of  sperm  case,  361 
Central  cylinder,  30-32. 
Cephalanthus,  418. 
Cercis,  410. 
Cereals,  393. 
Cetraria,  275. 
Chsetophora,  222,  229. 
Chalaza,  i. 
Chara,  228. 

Charophyceae,  209,  228. 
Chemosynthesis,  103. 
Cherry,  fruit,  192,  409. 
Chestnut,  190. 
Chicory,  419. 
Chicory  family,  419. 
Chlamydospores,  247. 
Chlorophyll,   38,   83-86,    103,    106, 

116,  211. 

Chloroplast,  86,  214,  220. 
Chocolate,  414. 
Chondrus  crispus,  243. 
Christmas  fern,  329,  330,  333. 
Chromatophore,  86. 
Chromoplast,  86. 
Cichoriaceae,  419. 
Cichorium  intybus,  419. 
Cinchonia,  418. 
Cinnamon  fern,  340. 
Citrange,  411. 
Citrous  fruits,  411. 
Citrus  aurantium,  412. 
Citrus  decumana,  412. 
Citrus  medica,  412. 
Citrus  nobilis,  412. 
Citrus  trifoliata,  411. 
Cladonia  cristatella,  271. 
Cladonia  rangiferina,  271,  272. 
Cladophora,  222,  229. 
Classification,  206-210. 
Clavariaceae,  298. 
Clayton's  fern,  340. 
Cleistogamous  flowers,  170. 
Clematis,  88. 
Climatic  factors,  424. 
Clostridium  pasteurianum,  125. 


482 


INDEX 


Clover,  410;  leaf,  74. 

Club  mosses,  346. 

Club  mosses,  giant,  355. 

Clusia,  29. 

Cluster  cups  of  barberry  rust,  280- 

282. 
Coal  deposits  by  fern  plants,  353- 

356. 

Cobalt  nitrate,  18,  91. 
Coca  butter,  415. 
Cockle  bur,  203. 
Coco,  415. 

Cocoanut-palm,  399. 
Cocos  nucifera,  399. 
Ccenocyte,  301. 
Coenocytic  mycelium,  301. 
Coffee  plant,  418. 
Coffeia  arabica,  418. 
Cold,  effects  of,  423. 
Coleochaete,  224-226,  229,  423. 
Collateral  bundles,  332. 
Collective  fruits,  188,  192-194. 
Columella,  249. 
Compass  plant,  78. 
Composite,  419. 
Composite  flowers,  153,  409. 
Compound  leaves,  73,  74. 
Concentric  bundles,  332. 
Cone-bearing  Gymnosperms,  357. 
Cone  fruit  of   Gymnosperms,   360, 

364- 

Cones  of  spruce,  357. 

Confervas,  221. 

Confervoideae,  209,  221,  229,  230. 

Conflict  of  species  in  plant  migra- 
tion, 438. 

Conidia,  247,  263,  264,  266,  267. 

Conidiophores,  257,  261,  266. 

Coniferales,  357. 

Conjugates,  209,  212. 

Conjugation,  216,  221,  222,  251. 

Copernicia  tectorum,  41. 

Coppice,  444,  445. 

Coral  fungi,  292,  298. 

Corchorus  olitarius,  413. 

Cordyceps  militaris,  261. 

Corludovica  palmata,  40x3. 

Conn,  44. 

Corn  grain,  8,  189. 

Corn  plant,  49,  397. 

Corn  seedling,  8-10. 

Corn  smut,  276,  277. 

Corn  stem,  structure  of,  52-54. 

Corolla,  143,  145,  149,  150,  154. 


Corolla,  irregular,  149. 

Corolla,  papilionaceous,  150,  151. 

Cortex,  31,  32. 

Cotton,  413,  414. 

Cotyledon,  2,  3,  5,  6,  10-13. 

Cranberry,  194,  416. 

Crataegus,  rust  of  leaves,  289. 

Crown  tubers,  26,  43. 

Crustaceous  lichens,  273. 

Cucumber,  419. 

Cucumis  melo,  419. 

Cucumis  sativus,  419. 

Cucurbita  pepo,  419. 

Cucurbitaceae,  418,  419. 

Cudbear,  275. 

Cup  fungi,  266,  267. 

Currants,  194. 

Cuscuta,  127. 

Cushion  type  of  plants,  450. 

Cuticle,  14,  46,  62,  84. 

Cyanophyceae,  209,  231. 

Cycas  revoluta,  401. 

Cycas     revoluta,    showing    macro- 

sporophylls,  367. 
Cyclosis,  228. 
Cynara  scolymus,  420. 
Cypripedium,  pollination  of,  179. 
Cystocarp,  240,  242. 
Cystopteris  bulbifera,  199,  328. 
Cystopus  candidus,  257-259. 
Cytase,  131,  135. 
Cytisus,  pollination  of,  178. 
Cytoplasm,  214. 

Dahlia,  19,  27. 

Dandelion,  419;  seeds  dispersal,  200. 

Darwin,  work  in  evolution,  458. 

Date  palm,  399,  400. 

Decay,  132,  133. 

Deciduous  shrubs  and  trees,  62. 

Dehiscent  fruit,  188,  191,  192. 

Deiutrification,  120.' 

Desert  societies,  427,  447. 

Defemids,  219. 

Desmodium,  203,  204. 

Diastase,  17,  107,  134,  135. 

Diatomeae,  209,  234. 

Diatoms,  234. 

Dichogamous  flowers,  175,  176. 

Dicotyledons,  56-60,  142-157,  207, 

403,  420. 

Dictyophora  duplicata,  300. 
Digestion,  go,  107,  135. 
Dimorphism  in  ferns,  338-340. 


INDEX 


483 


Dimorphism    in    gamete    plants    of 

Equisetum,  346. 
Dioecious,  237,   252,   253,  307,  349, 

376. 

Dioecious  flowers,  158. 
Dimorphic  flowers,  158. 
Dionaea  muscipula,  81. 
Diphtheria,  137,  138. 
Disk  flowers,  153,  154. 
Distribution  of  plants,  431. 
Dodder,  127. 

Downy  mildews,  256-259. 
Drapernaudia,  222. 
Drosera  rotundifolia,  81. 
Drupaceae,  407. 
Drupe,  192,  408. 
Drupelet,  192. 

Earth  stars,  299. 

Easter  lily,  44,  166,  401. 

Ecology,  421. 

Economic  plants,  392-420. 

Ectocarpus,  236. 

Ectoplasm,  214,  215. 

Edaphic  plant  societies,  451. 

Egg,  224,  225,  227,  230,  238,  240,  242, 

255,  258,  309,  310,  325,  336. 
Egg  apparatus  of  angiosperms,  382, 

384- 
Egg  case,   222-228,   230,   237,   238, 

240,  255,  258,  304,  308,  3I7-3I9> 

335,  365- 

Egg  case  of  pine,  363,  365. 
Elaters,  309,  311. 
Elaters  of  horsetail,  345. 
Elfin  tree,  450. 
Elm,  American,  405. 
Elm,  buds  and  snoots,  65. 
Elm  family,  405. 
Elodea,  98,  100. 
Emasculation,  of  flower,  468. 
Embryo,  1-13,  184-186,  385. 
Embryo  of  fern,  337~339- 
Embryo  sac,  184,  380-384. 
Endocarp,  188,  192,  194. 
Endodermis,  332. 
Endoplasm,  214,  215. 
Endosperm,  5-19,  185,  186, 362,  365. 
Endosperm  nucleus,  382. 
Endosperm  of  Angiosperms,  383. 
Energesis,  90. 
English  ivy,  29. 
Ensyme,  131. 
Entomosporium  maculatum,  407. 


Environment,   influence   on  plants, 

421. 

Epicarp,  188. 
Epidermis,  30,  31,  83-85. 
Epidermis,  outgrowth  of,  84. 
Epigaea  repens,  415. 
Epinasty,  79. 

Epipactis,  pollination  of,  173. 
Epiphegus,  87,  103,  128. 
Epithecium,  272. 
Equisetineae,  210,  343. 
Equisetum,  117,  352,  354,  355. 
Equisetum  arvense,  344. 
Equisetum  hyemale,  343. 
Ericaceae,  415. 
Eupatorium,  76. 
Evergreens,  62. 

Exalbuminous  seeds,  186,  386. 
Excipulum,  272. 
Evening  primrose,  flowers  of,  145; 

dwarf,  462;  Lamarck's,  461. 
Evolution,  of  an  individual,  456. 
Evolution  of  human  societies,  455. 
Evolution,  principles  of  plant,  455- 

463. 

Evolution,  steps  in,  457. 
Exocarp,  188,  192,  194. 

Factors,  ecological,  421. 

Fagales,  402. 

Fairy  club  fungi,  292,  298. 

Fascicled  roots,  27. 

Fehling's  solution,  18. 

Female  members  of  flower,  379,  380. 

Female  nucleus,  227,  258. 

Female  organ,  230,  240,  304,  379, 
380. 

Fermentation,  114, 133-135. 

Fermentation,  alcoholic,  114,  134. 

Ferments,  134,  135. 

Fern  leaf,  structure,  333,  334. 

Fern-like  plants,  343~3S6. 

Ferns,  327-342. 

Ferns,  bank  of,  425. 

Ferns,  life  history  of,  334-338;  for- 
mula for,  342. 

Ferns,  review  of,  341. 

Ferns,  sexual  organs,  335,  336. 

Fertilization,  182-184,  217,  222,  224, 
225,  227,  240,  242,  258,  336,  365, 
383,384- 

Fertilization  in  white  pine,  365. 

Fertilization,  of  rust  fungi,  281, 
282. 


484 


INDEX 


Fibro- vascular  bundles,  31,  42,  52- 
60,  64,  66,  332. 

Fibrous  roots,  27. 

Ficus  carica,  179,  180,  406. 

Fig,  406;  pollination  of,  179-181. 

Filamentous  green  algae,  221-226. 

Filicineae,  210,  327. 

Fissidens,  312. 

Fission  fungi,  136,  245. 

Fittonia,  81. 

Flax,  410. 

Flax  family,  410. 

Fleshy  fruit,  192,  408. 

Fleshy  roots,  29. 

Floral  shoot,  39,  140-166. 

Floret,  153. 

Flower,  complete,  144;  perfect,  144; 
polypetalous,  144;  receptacle  of, 
144. 

Flower,  evolution  of,  376;  dimor- 
phism of,  376;  structure,  377; 
members  of,  379,  380. 

Flower  head,  153. 

Flower,  members  of,  141,  142,  380. 

Flower,  parts  of,  141,  142. 

Flower,  primitive,  375." 

Flower  shoot,  140-166. 

Flowers,  structure  and  kinds,  140-166. 

Foliaceous  lichen,  271. 

Foliage  shoot,  39. 

Foliose  liverworts,  311. 

Foot,  of  fern  embryo,  337,  338. 

Forest,  kinds  of,  440;  structure,  441; 
longevity,  442;  relation  to  rain- 
fall, 442;  to  floods,  444;  regener- 
ation of,  444;  protection  of.  446. 

Forest  societies,  440. 

Franklinia  altamaha,  415. 

Fraxineus,  416. 

Freezing,  effects  of  on  plants,  48,  62, 

63,  423- 
Fruit,  187-197. 
Fruit  case,  242. 
Fruit  sugar,  18. 

Fruiting  spike  of  horsetail,  344,  345. 
Frullania,  312. 
Frustule,  234,  235. 
Fruticose  lichens,  271. 
Fucus,  236,  237. 
Funaria  hygrometrica,  320. 
Fungi,  characters,  246. 
Fungi,  classes  of,  247,  298. 
Fungi,  respiration  of,  112. 
Fungi,  theories  of  evolution  of,  302. 


Gametangium,  217,  251. 

Gamete,  217-219,  230,  251,  324. 

Gamete  bearer,  308. 

Gamete  plant,  324,  328,  345. 

Gamete  plant  of  pine,  361,  365. 

Gamete  plants  of  Selaginella,  349. 

Gametophore,  308,  312. 

Gametophyte,    219,    224,   324,   325, 
328,  380-384. 

Gamopetalous,  149,  157. 

Gamosepalous,  149, 157. 

Garden  sage,  pollination  of,  177. 

Gaultheria  procumbens,  415. 

Gaylussacia  resinosa,  415. 

Gelatinous  lichens,  273. 

Gemmae,  307. 

Geotropism,  22. 

Germ  diseases,  136-139. 

Geum,  203,  264. 

Gill  fungi,  292. 

Ginger  beer  plant,  270. 

Gihgko,  197,  371. 

Gladiolus,  165,  166. 

Gleditsia,  410. 

Glceocapsa,  232. 

Glucose,  1 8,  466. 

Glume,  159,  162. 

Golden  rod,  419. 

Gonidia,  of  fungi,  247. 

Goober,  410. 

Gordonia  lasianthus,  415. 

Gordonia  pubescens,  415. 

Gossypium  barbadense,  414. 

Gossypium  herbaceum,  414. 

Gourd  family,  418. 

Gourds,  418. 

Gracillaria,  242,  243. 

Grains,  393. 

Gramineae,  392. 

Grape  fruit,  412. 

Grape  mildew,  256. 

Grape  sugar,  18,  19. 

Grass  family,  392. 

Green  felts,  226-228. 

Ground  covers,  422. 

Ground  nut,  410. 

Guard  cells,  of  stomates,  83-86. 

Gymnospermse,  210,  357. 

Gymnosperms,  207,  357,  374. 

Gymnosperms,  fruits  of,   196,  364, 

369,  3?i. 

Gymnosperms,  primitive,  355. 
Gymnosperms,  review  of,  371. 
Gymnosporangium,  287-289. 


INDEX 


485 


Haematacoccus,  220,  229. 

Hairy  cap  moss,  317. 

Halophytes,  428. 

Hanging  moss,  273. 

Haustoria,  127-129,  257. 

Hazelnut,  190. 

Heart  wood,  59. 

Heat,  422. 

Heath  family,  415. 

Hedgehog  fungi,  292,  299. 

Helianthus  annuus,  153. 

Helianthus  tuberosus,  19,  420. 

Heliotropism,  25. 

Hemlock  spruce,  131. 

Hemp,  402-405. 

Henequen  plant,  405. 

Hepatica  hepatica,  304. 

Hepatica  triloba,  304. 

Hepaticse,  210,  304-315. 

Hercules'  Club,  298. 

Hermaphrodite,  237. 

Heterocyst,  233,  234. 

Hetercecism,  247. 

Heterothallic,  252,  253,  306,  349. 

Hibiscus,  413. 

Hickory  nut,  190. 

Hieraceum,  419. 

Hilum,  i,  4. 

Holdfast,  237. 

Holly  leaf,  71. 

Homothallic,  253. 

Honey  guides,  173. 

Honey  locust,  410. 

Hordeum  hexastichon,  396. 

Hordeum  vulgare,  396. 

Horned  liverworts,  210,  313-316. 

Horse  chestnut,  buds  and  shoots,  63, 

65. 

Horsetails,  343~346. 
Host  plant,  247. 
Houstonia,  175,  418. 
Huckleberry,  194,  415. 
Huckleberry  family,  415. 
Humus,  130,  132. 
Humus  saprophytes,  130. 
Hybrids,  meftdelian^459-46 1 . 
Hydrangea,  leaf  of/Vx 
Hydrodictyon,  221. 
Hydrogen,  15,  101,  118. 
Hydrophytes,  428. 
Hygrophytes,  428. 
Hymenium,  262,  269,  293. 
Hypha,  247. 
Hypococtyl,  2,  4,  10. 


Hyponasty,  79. 
Hypothecium,  272. 

Iceland  moss,  275. 

Impatiens,  56,  205. 

Imperfect  flowers,  174. 

Indehiscent  fruit,  188. 

Indian  corn,  397;  flowers,  158-162. 

Indian  corn,  bracing  roots  of,  29. 

Indian  corn,   races  of  for  oil  and 

starch,  466. 

Indian  lotus,  spiral  ducts  of,  54,  55. 
Indian  turnip,  44,  163-165. 
Indusium,  330,  331. 
Inorganic  compounds,  117. 
Insectivorous  plants,  81,  82,  89. 
Insects,  pollination  by,  172-184. 
Integument,  of  ovule,  183,  184,  361. 
Inulin,  19,  30;   sphaero-crystals   of, 

19,  3°- 

Involucre,  153. 
Iris,  42. 

Irish  moss,  243. 
Iron,  117,  118. 
Isoetes,  350,  352. 
Isoetineae,  210,  350. 
Ivy,  40,  41,  83. 
Ivy,  epidermis  of,  83. 

Jack-in-the-pulpit,  44,  163-165. 
Japanese  sago,  401. 
Jerusalem  artichoke,  19,  420. 
Juglandales,  403. 
Jungermannia,  313. 
Jungermanniales,  315. 
Jute,  413. 

Kalmia  latifolia,  pollination  of,  176, 

177,  4i5- 
Katabolism,  106. 
Kumiss,  270. 

Labellum,  173,  179. 

Labrador  tea,  415. 

Lactuca  scariola,  78,  201,  419. 

Lamarck's    evening    primrose,   148, 

461. 

Laminaria,  235,  236. 
Laminaria  angustata,  239. 
Laminaria  digitata,  235,  239 
Laminaria  japonica,  239. 
Laurel  leaf,  71. 

Leaf  arrangement,  68,  69,  76,  77. 
Leaf  diastase,  134. 
Leaf  divisions,  73,  74. 


486 


INDEX 


Leaf  glands,  81-85. 

Leaf  hairs,  81-85. 

Leaf,  parts  of,  51,  70,  71. 

Leaf  patterns,  81. 

Leaf  reduction  by  desert  plants,  449. 

Leaves,  fall  of,  75. 

Leaves,  form  of,  70-82. 

Leaves,  modification  of,  86-89,  449. 

Leaves,  movement,  77-82. 

Leaves,  relation  to  light,  77-81. 

Leaves,  respiration  of,  in. 

Leaves,  structure  of,  83-86. 

Leaves,  venation,  71,  72. 

Leaves,  work  of,  90-116. 

Ledum,  415. 

Legume,  152,  191,  409. 

Leguminosae,  152,  409. 

Lemanea,  241,  242. 

Lemons,  412. 

Len tides,  63,  in. 

Lepidodendron,  354,  355. 

Leptomitus  lacteus,  256. 

Lettuce,  419. 

Leucoplast,  86. 

Lianafe,  41. 

Lichens,  270-275;  use  of,  275. 

Lichens  in  soil  building,  273. 

Lichens,  structure,  274. 

Life  cycle,  218,  219,  259,  290,  325, 

342,  356,  374,  391- 
Life  factors,  424. 
Life   history   of   Angiosperms,  380; 


formula  for,  389. 
of  G 
mula,  374. 


Life  history  of  Gymnosperms,  for- 


Life  history  of  heterosporous  pterido- 

phytes,  formula,  356. 
Life  history  of  mosses,  326. 
Life  history  of  wheat  rust,  289;  life 

cycle  of,  290. 
Light,  422. 

Light,  importance  of,  78,  97-105. 
Ligule  of  corn  leaf,  51,  71. 
Ligustrum,  416. 

Lilac,  416;  buds  and  shoots,  65. 
Lilac  mildew,  263,  264. 
Liliaceae,  400. 
Liliales,  166. 
Lilium.  harrisii,  166. 
Lilium  longiflorum,  166. 
Lily  bulb,  44. 
Lily  family,  400. 
Linaceae,  410. 
Linaria  linaria,  148. 


Linaria  vulgaris,  148,  1-49. 
Linden  family,  413. 
Linun  usitatissimum,  410. 
Lipase,  135. 
Liverleaf,  304. 

Liverworts,  304-315,  325,  326. 
Loblolly  bay,  415. 
Locule,  of  anther,  143. 
Locust,  410. 

Lycopersicum  esculentum,  416. 
Lycopodineae,  210,  346. 
Lycopodium,  346. 
Lycopodium  cernuum,  347. 
Lycopodium    lucidulum,    199,    346, 
347- 

Macrocystis,  236. 

Macrosporangia  of  pine,  361,  362; 

of  angiosperms,  379. 
Macrosporangium  of  Cycas,  368;  of 

Zamia,  369. 
Macrospore,  348,  382. 
Madder  family,  418. 
Madders,  418. 
Magnesium,  117,  118. 
Maidenhair  fern,  fruit  dots  of,  328. 
Maidenhair  tree,  197. 
Maize,  158,  397. 
Male  gametophyte  of  angiosperms, 

380. 

Male  members  of  flower,  379,  380. 
Male  nucleus,  227,  258. 
Male  organ,  230,  240,  304,  379,  380. 
Mallow  family,  413. 
Malt  diastase,  134. 
Malvaceae,  413. 
Mandarins,  412. 
Manila  hemp,  402,  405. 
Maple  family,  412. 
Marchantia,  3Q4-311,  3*5- 
Marchantiales,  315. 
Marsilia,  41. 

Matteuccia  struthiopteris,  340. 
Medicago  denticulata,  122. 
Medulla,  57. 
Medullary  rays,  57,  60. 
Megaspore,  348,  382. 
Meiboreia,  203. 
Melampsorella  cerastii,  280. 
Mendelism,  459. 
Mendel's    law,    relation    to    plant 

breeding,  476. 
Meristem,  32. 
Mesocarp,  188,  194. 


INDEX 


487 


Mesophytes,  426. 
Mesquite  tree,  28. 
Metabiosis,  125. 
Metabolism,  106,  117. 
Metroxylon  laevis,  400. 
Metroxylon  rumphii,  400. 
Micrococcus,  135,  245. 
Microcycas,  370. 

Micropyle,  i,  183,  361,  381,  386. 
Microsphsera  alni,  263,  264. 
Microsporangia,  379,  380. 
Microspore,  248,  360. 
Microspores,  of  pine,  360. 
Microsporophyll     of     Angiosperms, 

379- 
Microsporophyll  of    Cycas,  367;   of 

Zamia,  368. 

Microsporophylls,  360,  379. 
Migration  of  plants,  431. 
Mildews,  246,  256-260,  262-265. 
Mimosa,  410. 
Mimosa  pudica,  80. 
Mistletoe,  128. 
Mitchella,  418. 
Mnium,  318. 
Molds,  132,  246-256. 
Molds,  conjugating,  248. 
Monilia,  267. 
Monocotyledons,     51-56,     158-166, 

207,  392-402. 

Monoecious,  237,  253,  376. 
Monotropa  uniflora,  86,  103,  130. 
Moraceae,  405. 
Morchella,  268,  269. 
Morels,  268,  269. 

Morphology,  206;  comparative,  206. 
Mosses,  316-326. 
Mother  cell,  224,  320,  325,  342,  356, 

374,  39  !• 
Mountain  laurel,  415;  pollination  of, 

176,  177- 

Mucor  mucedo,  252,  253. 
Mucor  stolonifer,  250. 
Mucorales,  253. 
Mucorineae,  253. 
Mulberry  family,  405. 
Musa  paradisiaca,  402. 
Musa  textilis,  402,  405. 
Muscarine,  296. 
Muscineae,  210,  316-326. 
Mushrooms,  291-296. 
Mushrooms,    cultivated,    291,    293; 

poisonous,  291,  295,  296. 
Muskmelons,  419. 


Mutation,  461-463. 
Mycelium,  129,  132,  247,  250-294. 
Mycorhiza,  124-127,  130,  347. 
Mycorhizae,  ectotropic,  1 24. 
Mycorhizae,  endotropic,  124. 
Myrsiphyllum,  46. 

Natural  selection,  459. 
Naval  orange  tree,  411. 
Nectar,  172;  nectaries,  172;  nectar 

glands,  172. 
Needle  leaves,  88. 
Nemalion,  239,  240,  242. 
Nettle  family,  404. 
Neuter  flowers,  156. 
Nicotiana  tabacum,  417. 
Nitella,  228. 
Nightshade  family,  416. 
Nitrate  bacteria,  103,  120. 
Nitrates,  103,  107,  118,  120. 
Nitrification,  119-126. 
Nitrite  bacteria,  103,  120. 
Nitrites,  103. 
Nitrobacter,  120. 
Nitrogen,  15,  100,  in,  119-123. 
Nitrogen,  fixation  of,  120-123. 
Nitromonas,  120. 
Nostoc,  233,  245,  273,  274. 
Nucellus,  5. 
Nucleolus,  213. 
Nucleus,  213,  214,  215,  231. 
Nutmeg  melons,  419. 
Nutrition  of  plants,  117-139. 
Nuts,  190,  404. 

Oak,  buds  and  shoots  of,  67. 

Oak  stem,  structure  of,  53,  60. 

Oat  flowers,  162,  163. 

Oat  smut,  277. 

Oats,  395. 

CEdogonium,  223,  224,  229,  230. 

(Enothera  biennis,  145. 

(Enothera  laevifolia,  462. 

(Enothera  lamarkiana,  148,  461,  462. 

(Enothera  nanella,  462. 

Oil,  18. 

Olea  europaea,  416. 

Oleaceae,  416. 

Olive  family,  416. 

Olive  tree,  416. 

Onagra  biennis,  145. 

Onion  bulb,  43. 

Onoclea  sensibilis,  329,  339. 

Onoclea  struthiopteris,  340. 


488 


INDEX 


Oogonium,   221-228,  230,  237,  238, 

255- 

Oosphere,  228. 
Oospore,  219,  222,  224. 
Ophioglossales,  351. 
Ophioglossum,  351. 
Oranges,  412. 
Orchid  family,  166. 
Orchidaceae,  166. 
Orchids,  velamen  of  roots,  28. 
Orchil,  275. 

Organic  compounds,  117. 
Origin  of  species,  459. 
Oryza  sativa,  396. 
Oscillatoria,  233,  245. 
Osmic  acid,  19. 
Osmosis,  48. 

Osmunda  cinnamomea,  340. 
Osmunda  claytoniana,  340. 
Osmunda  regalis,  340. 
Ostrich  fern,  340. 
Otthia  morbosa,  266. 
Ovary,  143,  184,  187,  375,  542. 
Ovule,  143,  183,  184,  361,  375. 
Ovule  case,  375. 
Ovule,    integuments    of,    185,    187, 

363- 

Oxycoccus  macrocarpus,  416. 
Oxy coccus  oxy coccus,  416. 
Oxydendrum  arboreum,  415. 
Oxygen,  15,  98-105,  116. 

Palea,  159,  162. 

Palm  family,  399. 

Palmaceae,  399. 

Pandanus,  81. 

Pandorina  morum,  221,  229. 

Papilionaceae,  152,  409. 

Parasites,  126-139,  246,  439. 

Parasites,  nutrition  of,  127. 

Parasitic  fungi,  nutrition  of,  129. 

Parenchyma,  31,  53,  54,  59,  85. 

Parmelia,  271. 

Parsnip,  26,  43. 

Parthenogenesis,  256. 

Pea,  7,  n,  18. 

Pea  family,  409. 

Pea  leaf,  74. 

Pea,  sweet.  150-152. 

Peach,  buds  and  shoots  of,  66,  67. 

Peach,  fruit,  192,  407. 

Peanuts,  409,  410. 

Pears,  195,  406,  407. 

Peat  mosses,  322-324. 


Peltigera,  271. 

Pepo,  195,  196. 

Perennial  stems,   structure    of,    c*. 

n       s  *        OO) 

58-60. 

Perennials,  37. 
Perianth,  165,  166,  375. 
Pericarp,  188,  192,  195. 
Pericycle,  31. 
Periplasm,  258. 
Perisperm,  185,  186,  385. 
Perisporiales,  262. 
Perithecium,  261-266. 
Peronospora  alsinearum,  258,  259. 
Peronospora  calotheca,  257. 
Peronospora  schleideniana,  258. 
Petal,  143. 
Petiole  of  leaf,  70. 
Peziza,  266. 

Phaeophyceae,  209,  235-239. 
Phallin,  296. 
Philotria,  98. 
Phloem,  31,  54-58. 
Phoenix  dactylifera,  399. 
Phoradendron  flavescens,  128. 
Phosphate  rock,  119. 
Phosphates,  118. 
Phosphorus,  15,  117. 
Photosynthesis,  85,  90,  97-105,  116. 
Phragmidium  violaceum,  282. 
Phycomyces  nitens,  253. 
Phycomycetes,  209,  247,  300. 
Phyllitis  scolopendrium,  328. 
Phylloclades,  46. 
Phyllotaxy,  68,  69,  76,  77. 
Physcia  stellaris,  271,  272. 
Physical  factors,  422. 
Phytomyxa  leguminosarum,  121. 
Picea,  cones  of,  357. 
Pileus,  293. 
Finales,  35  7. 
Pine  leaves,  75. 
Pine,  life  history  of,  360. 
Pine  seed,  10,  364,  366. 
Pine  seedling,  10,  103. 
Pineapple  family,  401. 
Pinus  sylvestris,  structure  of  wood, 

358. 

Piper  nigrum,  seed  of,  185. 
Pirus,  407. 
Pistils,  143,  147,  150,  151,  J55,  162, 

166,  379. 

Pitcher  plant,  88,  89. 
Pith,  57,  59- 
Pits,  bordered,  358,  360. 


INDEX 


489 


Plankton,  234. 

Plant  breeding,  principles  of,  464- 
478. 

Plant  kingdom,  207. 

Plant  migration,  431;  by  seeds,  432; 
by  fruits,  432;  by  layering,  433; 
fertility  of  species,  434;  by  physi- 
cal and  chemical  conditions  of  soil, 
4355  by  climatic  changes,  435. 

Plant  societies,  439-454. 

Plasmopora  viticola,  256. 

Platycerium  alcicorne,  338,  339. 

Pleurococcus  vulgaris,  220,  229,  273, 
274. 

Plowrightia  morbosa,  265,  267. 

Plum  family,  407. 

Plum,  fruit,  192,  408. 

Plum  rot,  267. 

Plums,  408. 

Plumule,  2,  7,  8. 

Pod,  152,  191,  409. 

Pogonatum,  321. 

Poison  ivy,  29. 

Poisonous  mushrooms,  291,  295,  296. 

Pollen,  147,  148,  167-184. 

Pollen  grain,  182-184,  360,  365,  368- 
370,  379>  380. 

Pollen  tube,  182-184,  365,  370,  379. 

Pollination,  167-184. 

Pollination,  artificial,  468. 

Pollination,  close,  169-171;  cross, 
169, 171-184. 

Pollinium,  168,  177. 

Polymorphism,  247. 

Polypodiaceae,  330. 

Polypodium  vulgare,  329. 

Polypody  fern,  330;  fruit  of,   329. 

Polyporaceae,  296. 

Polyporus  applanatus,  298. 

Polyporus  borealis,  131. 

Polyporus  igniarius,  298. 

Polyporus  mollis,  132. 

Polyporus  pinicola,  297. 

Polysiphonia,  241,  242,  324. 

Polystichum  acrostichoides,  330. 

Polytrichum,  317. 

Pomaceae,  406. 

Pome  fruit,  195,  407. 

Pomelo,  412. 

Populus  dilitata,  48. 

Pore  fungi,  292,  296-298. 

Postelsia,  236. 

Potassium,  117,  118. 

Potato,  44,  416. 


Potato  family,  416. 

Powdery  mildews,  262-265. 

Prairie  societies,  446. 

Prickly  ash,  411. 

Prickly  lettuce,  78,  200,  201. 

Primrose,  evening,  145-148;  La- 
mark's,  461;  dwarf,  462. 

Privet,  416. 

Procarp,  240. 

Promycelium,  275,  277,  279,  284, 
285. 

Pronuba,  pollination  by,  171. 

Prop  roots,  29. 

Protease,  135. 

Proteid  grains,  14,  15. 

Proteids,  19. 

Prothallium  of  angiosperms,  380. 

Prothallium  (female  gamete  plant) 
of  Cycas,  368. 

Prothallium     of     ferns,    329,    334, 

335- 

Prothallium  of  Selaginella,  348,  349. 
Prothallus,  329. 
Protococcoidese,  209,  220,  230. 
Protococcus  vulgaris,  220. 
Protonema,  316,  320,  321,  325,  334, 

34°. 

Protoplasm,  13,  33-35,  182,  213-217. 
Prunes,  408. 

Prunus  amygdalinus,  408. 
Prunus  persica,  407. 
Prunus  serotina,  409. 
Pseudomonas  radicicola,  121. 
Pteridium  aquilinum,  330. 
Pteridophyta,  207,  210. 
Pteridophytes,  207. 
Pteris    aquilina,    330;    germinating 

spores,  334. 
Pteris  cretica,  340. 
Pteris    serrulata,    embryo    of,    337, 

339- 

Pteris  serrulata,  spore  of,  334. 
Ptomaines,  133. 
Ptyalin,  134. 
Puccinia  graminis,  280. 
Puccinia  malvacearum,  290. 
Puccinia  podophylli,  290. 
Puccinia  rubigo-vera,  287. 
Puccinia  taraxaci,  290. 
Puffballs,  292,  299. 
Pumpkin  seed,  7. 
Putrefaction,  133. 
Pyrenoid,  213,  214. 
Pyxidium,  192, 


490 


INDEX 


jrcus  alba,  208. 
icrcus  coccinea,  208. 

jrcus  rubra,  208. 
lillworts,  350. 
Hiinine,  407,  418. 

Races  of  plants,  464,  465. 

Radicle,  2,  5,  7-11. 

Ramie,  405. 

Ranunculus  acris,  142,  143,  187. 

Raphe,  i,  184. 

Raspberries,  42,  192-195,  202,  406. 

Rattan,  40.    • 

Ray  flowers,  156. 

Records,  in  plant  breeding,  478. 

Red  algae,  239-242;  uses,  243. 

Red  bud,  410. 

Red  rust  of  wheat,  282. 

Red  snow  plant,  220. 

Reindeer  moss,  271,  272. 

Reinforced  fruits,  188,  195. 

Respiration,  85,  90,  108-116. 

Respiration,  conditions  of,  112. 

Rhabdonia,  242,  324. 

Rhizobium  leguminosarum,  121. 

Rhizoids,   249,   250,  305,  306,  321, 

335- 

Rhizome,  41,  333. 
Rhizopus  nigricans,  248-251. 
Rhodochytrium,  211. 
Rhododendron  catawbiense,  415. 
Rhododendron  maximum,  415. 
Rhododendrons,  93,  94,  140,  415. 
Rhodophyceae,  209,  239. 
Rhus  hirta,  67. 
Rhus  typhina,  67. 
Riccia,  304,  311,  315. 
Rice,  396. 
Richardia,  165. 
Rings,  annual,  53,  59,  60. 
Robinia,  410. 
Roccella  tinctoria,  275. 
Rock  weed,  236,  237. 
Root  absorption  in  desert,  449. 
Root  cap,  30,  32. 
Root  climbers,  40. 
Root  hairs,  30-36. 
Root  pressure,  95. 
Root  sheath,  8,  9,  13. 
Root  stocks,  41,  42,  330. 
Root  systems,  26^-28. 
Root  tubercles,^  1-123. 
Root  tubers,  29,  45. 
.Roots,  1-12,  26-32. 


Roots,    growth    of,    20-25;    motor 
zone,  21,  22;  perspective  zone,  21, 

22. 

Rosaceae,  406. 

Rose  family,  406. 

Rose  leaf,  74. 

Rosette  plants,  450. 

Rosettes,  81. 

Royal  fern,  340. 

Rubber  plant  leaf,  72. 

Rubiaceae,  418. 

Rubiales,  418. 

Rust  fungi,    279-290;   losses   from, 

279. 

Rutaceae,  411. 
Rye,  395- 

Sac  fungi,  261-275. 

Sac  fungi,  life  history  of,  275. 

Saccharomyces  ceriviseae,  114,  115, 

268. 

Saccharum  omcinarum,  398. 
Sago,  401. 
Sago  palm,  401. 
Salicales,  403. 
Salsify,  419. 
Saltpeter,  119. 
Samara,  189. 
Sand  dunes,  452. 
Sap  wood,  59. 
Saprolegnia,  254-256. 
Saprophytes,  129-139,  246. 
Saprophytes,  nutrition  of,  130. 
Saprophytic  fungi,  136,  248. 
Sarcina,  135,  245. 
Sargasso  sea,  238. 
Sargassum,  238. 
Scale  leaves,  87,  89. 
Schizocarp,  189. 
Schizomycetes,  209,  245. 
Schizophyceae,  245. 
Sclerenchyma,  332. 
Sclerotinia  fructigena,  267,  268. 
Scolopendrium  vulgare,  328. 
Scouring  rush,  343. 
Screw  pine,  30,  81. 
Scutellum,  9,  13. 
Seaweeds  at  low  tide,  454. 
Secale  cereale,  395. 
Seed,  1-20. 

Seed  case,  of  angiosperms,  378. 
Seed  coats,  1-12. 
Seed,  development  of,  182. 
Seed,  formation  of,  185. 


INDEX 


49 i 


Seed,  of  pepper,  185. 
Seed  plants,  207,  357-391- 
Seedlings,  1-12;  respiration  of,  108- 

ui. 

Seeds,  dispersal,  198-205. 
Seeds,  food  in,  11-19. 
Seeds,  germination  of,  1-12. 
Seeds,  grapplers  on,  202-204. 
Seeds,  synopsis  of  parts,  386. 
Selagiriella,  347~349>  35 2- 
Selaginella  rupestris,  350. 
Selection,   in   plant   breeding,'  469 

472. 

Sensitive  fern,  329,  339. 
Sensitive  plants,  80,  410. 
Sepal,  142. 

Sequoia  sempervirens,  445. 
Sequoia  washingtoniana,  442,  445. 
Sexual  reproduction,  216,  217,  224, 

225,  237,  239,  251,  255,  258,  264, 

379,  380. 
Shaddock,  412. 
Sheath  of  corn  leaf,  51,  71. 
Shoots,  characters  of,  63. 
Shoots,  winter  condition  of,  61-69. 
Sigillaria,  354,  355. 
Silicon,  117. 
Silique,  192. 

Silphium  laciniatum,  78. 
Simple  leaves,  73. 
Siphon  algae,  226-228. 
Siphonales,  230. 
Siphoneae,  209,  226. 
Sisal,  sisal  hemp,  405. 
Smilax,  46. 
Smut  fungi,  276-279. 
Smut  spores,  germination,  277,  285. 
Solanaceae,  416. 
Solanum  tuberosum,  416. 
Solidago,  419. 
Soredia,  271. 
Sorghum,  398,  399. 
Sour  wood  tree,  415. 
Spadix,  163,  164. 
Spanish  needles,  203. 
Spartium,  pollination  of,  178. 
Spathe,  164. 
Sperm  case,  222-228,  230,  237,  238, 

240,  242,  258,  304,  308,  317,  335, 

361,  379- 

Sperm  case  of  pine,  361,  365. 
Sperm  cases  of  Zamia,  370. 
Sperm  cells,  182-184. 
Spermatophyta,  207,  210,  375. 


Spermatophytes,  375. 

Spermogonia  of  barberry  rust,  281, 

282. 
Sperms,  222,  224,  227,  230,  238,  325, 

335,  336,  365- 
Sperms  of  Zamia,  369,  370. 
Sphseriales,  265. 
Sphagnales,  322. 
Sphagnum,  323. 
Sphagnum  moors,  322. 
Spikelets,  158,  162. 
Spirillum,  135,  245. 
Spirogyra,  98^212-219.  | 
Sporangiophore,  249^ 
Sporangium,  249,  253. 
Sporangium  fruit  fungi,  248-260. 
Sporangium  of  ferns,  330. 
Sporangium  series  of  fungi,  247,  300. 
Spore  case,  242,  249,  253,  255,  330, 

348. 

Spore  case  fungi,  247,  300. 
Spore  case  of  angiosperms,  379. 
Spore  case  of  ferns,  330,  331. 
Spore  of  horsetail,  345. 
Spore  plant,  324,  328. 
Spores,   asexual,   247;  germination, 

251- 

Spores  of  ferns,  331,  334. 
Spores  of  liverworts,  310,  311. 
Spores  of  mosses,  320,  321. 
Sporidia,  276,  277,  284. 
Sporocarp,  226. 
Sporofinia  grandis,  253. 
Sporogonium,   309,   310,   313,   315, 

3J9- 

Sporophores,  247,  249,  256,  257. 
Sporophyll  of  fern,  339. 
Sporophyll  of  horsetail,  345. 
Sporophyll  of  pine,  360. 
Sporophyll  of  Selaginella,  347,  348. 
Sporophyte,  219,  224,  324,  325,  328, 

375- 

Spurge  family,  4. 
Squash,  195,  196,  419. 
Squash  seed,  7,  n. 
Stamens,   143,   145,   150,   151,   154, 

159,  166. 
Stamens,    dimorphic,    150;    diadel- 

phous,    151;    syngenesious,     154, 

176. 

Stamens  of  pine,  360,  361. 
Staminate  cone  of  pine,  360,  361. 
Starch,  15-17, 97-107;  testfor,  15-17. 
Starch  grains,  14-17,  213,  214. 


492 


INDEX 


Stem,  function  of,  38;  types  of,  37-50. 

Stems,  climbing,  40. 

Stems,  coiling,  41. 

Stems,  crown  or  acanlescent,  42,  43. 

Stems,  decumbent,  42. 

Stems,  definite  and  indefinite  growth, 

49. 
Stems,    elongation,     21;     direction 

growth,  20,  23,  25. 
Stems,  growth  of,  49,  50. 
Stems,  structure,  51-60.    -^_ 
Stems,  twining,  41. 
Sterigmata,  293,  294. 
Stigma,  143. 

Stink  horn  fungi,  299,  300. 
Stipe,  293. 

Stipules,  66,  70,  71,  74. 
Stolon,  41. 
Stomates,  83-85. 
Stomates,  number  of,  95. 
Stone  fruit,  188,  192. 
Stone  mountain,  444. 
Stoneworts,  228. 
Strangling  roots,  29. 
Strawberries,  41,  195,  406. 
Streptococcus,  135. 
Strobilus  of  club  moss,  346-348. 
Style,  143. 

Succulent  stems,  45,  46. 
Sucrose,  18. 

Sugar,  18,  97-107;  test  for,  18. 
Sugar  beet,  18. 
Sugar  cane,  18,  398. 
Sugar  maple,  18,  412. 
Sulphates,  118. 
Sulphur,  15,  117. 

Sumac,  buds  and  shoots  of,  67,  68. 
Sundew,  81,  82. 
Sunflower,  153-15?,  4iQ- 
Sunflower  stem,  structure  of,  56-58. 
Sweet  potato,  30,  45. 
Swimming  spores,  222. 
Symbiont,  125. 
Symbiosis,  124-127,  270. 
Symbiosis,  antagonistic,  125. 
Symbiosis,  contact,  125. 
Symbiosis,  mutualistic,  125. 
Synergids,  382-384. 
Syringa,  416. 

Taka  diastase,  134. 
Tangero,  412. 
Tap  roots,  27. 
Taraxacum  densleonis,  419. 


Taraxacum  taraxacum,  419. 

Taxodium,  442. 

Taxus,  196,  359,  388. 

Taxus  canadensis,  359. 

Tea  family,  415. 

Teleutospore,  281-285. 

Temperature,  influence  on  respira-- 

tion,  112. 

Tendril  climbers,  40. 
Tendrils,  40,  88. 
Tendrils,  irritability  of,  81. 
Tendrils  of  sweet  pea,  88. 
Tetraphis  pellucida,  320. 
Tetraspores,  242. 
Thallophyta,  207,  209. 
Thallophytes,  207,  211. 
Thallose  liverworts,  306. 
Thea,  415. 
Theaceae,  415. 
Theobroma  cacao,  414. 
Thistle  family,  419. 
Tick  trefoil,  203,  204. 
Tilia  americana,  413. 
Tiliaceae,  413. 
Tillandsia,  273,  400. 
Tilletia  tritici,  278,  279. 
Tissue,  14,  54-60. 
Toadstools,  292. 
Tobacco,  417. 
Tomato,  194,  195,  416. 
Tooth  fungi,  292,  299. 
Touch-me-not,  205. 
Tracheides,  358,  359. 
Tradescantia,  28,  29. 
Tragopogon  porrifolius,  419. 
Trametes  pini,  132. 
Transpiration,  90-96. 
Trees,  age  of,  442. 
Trichodesmium  erythraeum,  231, 
Trichogyne,  225,  240. 
Trifolium,  410. 
Trillium,  41. 
Triticum  ovatum,  393. 
Tropaeolum  leaf,  73. 
Tropophytes,  429. 
Trumpet  creeper,  29. 
Tryptic  ferment,  134. 
Tuber,  44. 

Tubular  flowers,  153,  154. 
Tundra,  272,  273,  450. 
Turgescence,  34. 
Turgor,  35,  215.^ 
Types  of  vegetation,  425. 
Typhoid  fever,  136-139. 


INDEX 


493 


Ulmaceae,  405. 
Ulmus  americana,  405. 
Ulothrix  zonata,  222. 
Unit  characters,  461,  477. 
Uredospores,  282-284. 
Uromyces  caryophyllinus,  1 29. 
Urticaceae,  404. 
Usnea  barbata,  273. 
Ustilago  avenae,  277. 
Ustilago  hordei,  277,  278. 
Ustilago  tritici,  277. 
Ustilago  zeae,  276,  277. 

Vacciniaceae,  415. 
Vaccinium  macrocarpon,  416. 
Vaccinium  oxycoccus,  416. 
Vaccinium  vitisidaea,  416. 
Variation  in  plants,  how  produced, 

467. 
Varieties,  production  of  new,  467; 

objects  in,  472. 
Vaucheria,  226-228,  230,  301. 
Veil,  of  mushroom,  294. 
Veins,  of  leaf,  71,  72. 
Venus  flytrap,  81,  88. 
Veratrum  viride,  69,  76. 
Vetch,  root  tubercles  of,  121. 
Vibrio,  135,  245. 
Viburnum  opulus,  172. 
Violet  seed,  185. 
Viscum  ablum,  128. 
Vitis-Idaea  vitisidaea,  416. 
Volva,  295. 

Walking  fern,  42,  327. 

Walnut,  190,  403. 

Walnut  order,  403. 

Wandering  Jew,  28,  29. 

Water  hyacinth,  30. 

Water  molds,  254-256. 

Water  net,  221,  229. 

Water  storage  by  desert  plants,  449. 

Watermelon,  419. 

Wheat,  393-395- 


Wheat  grain,  section  of,  14. 

Wheat  rust,  280-287;  races  of,  285; 

history  of,  286;  prevention  of,  287. 
Wheat  smut,  loose,    277;  stinking, 

278,  279. 

White  rust,  256-259. 
Willow,  buds  and  shoots  of,  68. 
Willow  mildew,  262. 
Willow  order,  403. 
Wind,  422,  423. 
Wintergreen,  415. 
Witches'  broom,  280. 
Wood-destroying  fungi,  131. 
Wood,  porosity  of,  59,  60. 
Woody  portion  of  vascular  bundle, 

3i,  53-58.  f 
Wound  parasite,  131. 

Xanthoxylum,  411. 
Xerophytes,  426. 
Xylem,  31,  54-58. 

Yeast,  fermentation  by,  114;  growth, 

115,  268. 
Yew,  American,  staminate  cones  of, 

359- 
Yucca,  pollination  of,  171. 

Zamia,  369-371,  401. 

Zamia,  female  gamete  plant,  370; 

egg  cases,  371. 

Zamia,  germination  of  pollen,  370. 
Zamia,  male  gamete  plant,  370. 
Zea  mays,  397. 

Zonal  distribution  of  plants,  453. 
Zob'gonidia,  222,  223,  225. 
Zobspores,  222,  225,  236,  254. 
Zygospore,  216-219,  221,  251-253. 
Zygnema,  219. 
Zygospores,  216,  217-219,  221,  222, 

251,  252. 
Zygote,  217,  219,  224,  325,  342,  374, 

39i. 
Zymase,  135. 


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